Yes, yet another Idea list, But a little different this time.

They might be adding this with the "cursed cannonballs", but I would love to see different types of cannon ammunition. I'll work with you and add ideas in the format you used above. I hope everyone else will as well.

-New cannon munition types
The pirates of old didn't just fire the round-shot we use in the game today. They used grape-shot (basically an anti personnel, close range shotgun round for ships), explosive shot, chain shot and other more creative ones besides. Here is a link to a full list of ideas if you want to browse over this in detail. https://www.seaofthieves.com/forum/topic/36803/cannon-ammunition-types

-Crow's nest buff
So, I want to see the crow's nest have more utility, because as it stands almost no one goes up there due to the long travel time up, and lack of any real advantage (you can mostly see fine from down on the deck). There is currently a glitch if you stand on the yard arms of the sails, where you wont bob with the ship and thus your eye of reach and spyglass have zero wobble. Not only that, but it seems that while standing on the yard arm the first part of a riddle is revealed once you hit the island banner. These properties should be transferred to the crow's nest. It would give sniper's a spot to be on the ships.

-Add new ship Man-o-War
This is way too long to go into detail about, details here https://www.seaofthieves.com/forum/topic/29992/a-ship-even-bigger-than-the-galleon/22 if you want a summary of the ship and its purpose, here. Four decks, with much larger (taller) sails. HORRIBLE turning and sluggish speed, but with 7 cannons on each side and with 4 of each of those protected by the hull of the ship you can blast other ships out of the water with ease, the problem is getting them in your sights. A sloop would be able to run circles around a Man-o-War. It could be a 5-6 player ship, but to truly be piloted it would really need 7-8 but I'll leave that to the QA team at Rare for balancing.

-The Ferry of the Damned as a boss fight
So, basically once every in-game month, during the full moon, the Ferry would rise from the depths as a galleon-esque ship with the appropriate amenities (cannonball barrels, working cannons, sails, and such). It would trap those who died on the server aboard (up to four at a time) until a new soul came to take their place on the Ferry. The Ferry would be driven around trying to take out other ships, and since the time span of it being on the sea is so small (just under 10 minutes if I'm not mistaken) It would be two and a half times faster than any other ship in the game at full speed, with the wind. It could take damage just like a normal ship but would fill up with mist instead of water, and its supplies would be unlimited. Finally if sunk, it would drop a cursed chest that could be turned in to any of the trade factions for a huge payout. The chest would have some huge dramatic effect, such as summoning a storm on your location, or maybe calling the kraken (where ever it is on the map) straight for you.

-Grappling hook as weapon
A length of rope with the hook attached at the end, you could twirl the hook to full speed after a few seconds with twirl speed equaling distance covered by the thrown hook. The hook would latch to whatever it hit, be that a player ship or cliff. Maybe rope physics will be hard to implement in this game i don't know I'm just suggesting this, but anyway. You could climb the rope and pull your self (or other attached players).This could allow for dynamic boardings from places other than the ladders, cinematic escapes, and more opportunities to explore. The grappling hook, due to its potential, would not be an equipment that can be used over and over, but instead a slot in your weapons with two uses (one initial grapple and then one back up).

-Royal Navy PVP faction and player bounties
At each outpost, perhaps in their own little building, a puffed up "too-important-to-look-at-you" kinda guy will reside. He is a part of the Royal Navy, sent to impose the crown's rule on the Sea of Thieves. To do this, the crown has placed a bounty of 5 gold on anyone who kills (you accrue 5 gold in your passive bounty for every kill) and 20 gold for the destruction of sea vessels (20 gold added to your passive bounty for every ship you sink). This would make you the target of bounty hunters (other players) looking to cash in on your reward money. Other players could also add to your bounty if you have slighted them somehow by putting up their own money at the Navy Officer. Your bounty would follow your account much like your owned gold does. To recover a bounty, one must approach the Navy Officer and buy a wanted poster/voyage from him. The wanted poster will randomly select a player on the server outside your crew and find their bounty, and the closest island to them. The wanted poster will display their worth after being sunk (killing them is not enough you must fully sink their ship). And the nearest island they were at, at the time of you accepting the bounty from the Officer, will be displayed as a (last seen near). The wanted poster will then appear in your hands as a physical item (looking like a rolled piece of parchment maybe?) You must then turn this in for the bounty to be collected. the bounty is split evenly amongst the crew, the higher the bounty the higher the rep bonus with the Royal Navy.

-Burying your treasure
A lot of people say there is no point to this in the current game, but with one change to the current dynamic of it, it can become something great. Say you find a captain's chest. You can go turn that in for say a thousand gold, or 10% of its value every day. That is what you get for burying your treasure, versus turning it in right away. You can bury up to 5 chests at any point (your gold hoarders reputation divided by 10 rounded down). Only certain spots can have chest buried and can be seen with a special looking glass/monocle/see-through gem. These spots automatically can have riddles generated for them, by the game. These riddles would all be rolled into one long voyage placed in a bottle to be found by anyone. So, someone could find a bottle that starts a voyage to find the Buried Stash1 / Cache2 / Treasure3 / Hoard4/ Trove5 of Sandmanbakery. So, you could make 10% off your buried treasure every day, or turn it in, but the danger being that if someone comes along and finds all your buried treasure you have to go and bury your new plunder all over again.

-New weapon Hand-cannon
A large, two handed cannon, smaller than the ship cannons, but still large. It would have 1 shot that acts exactly like a cannonball. You move very slowly, and the time it takes to have the hand cannon ready to fire would be a few seconds after your character has stopped moving. this is the time it takes for your character to lug the heavy piece of iron into a shooting position that's stable enough to be aimed, and would give other players time to react to having the threat of a cannonball to the face become more likely. Cannot reload with normal cannonballs as it is a slightly smaller ball.

-New weapon Rapier and Buckler
The gentleman's sword, a thin blade made more for stabbing than slashing, the rapier would be able to land many more hits than the cutlass, but would do approximately 8 percent damage. To make up for the lack of damage, a rapier would have a longer combo of 4 and have a much quicker block ready animation to lift the buckler into position. This weapon would most likely be used more as a crowd control than actual damage output.

-New weapon Boarding Axe
You've seen this elsewhere on the forums I bet, a two handed axe meant as a heavy weapon, dealing 31 percent damage but taking much longer to get a swing off (maybe a full 3 seconds equals 1 swing?) A power swing would deal 70% damage? The specialty of the boarding axe though, is it's ability to knock holes in ships from the inside. Once inside an enemy ship you can hack off repair boards (can't hack into smooth wood) to pry them off. This would take 3 power swings each, making a large chopping sound to alert the crew. Can block but has a longer ready time than the cutlass.

-New weapon Grenade
Now this could maybe replace the Hand-cannon, but i think the range of the other would make up for this one's lack thereof. The grenade could maybe get 5 meters away as they would be very heavy, and you could carry 3. They can put hole's in ships, but can be picked up by the enemy to be thrown overboard. Not only that, they have a long fuse, so you have to light them and then wait to throw them for a perfect, timed explosion, or throw them and run. They would have an AoE of damage equal to half a cannonball and half the damage to a player. the fuse should be about 7 seconds? While holding a grenade and cocking it for the throw (same animation) you walk much slower and turn slower.

-Duel-wielding weapons
I think it's funny that we can't have two of the same weapon in our weapon slots. If I want to hold two pistols why can't I? I would love to duel-wield two pistols at the same time. I can only hip fire, as the button for aiming is now used to fire the other pistol, but hey. This would also go for the other weapons as well. If it takes up two hands, then just have switching between weapons be just that. Have two Eyes of Reach for a one man firing squad, or double cutlass for double the attacks, but no blocking.

-New weapon Musket
Very similar to the Eye of Reach, just without the scope and 75% damage instead of 80%. This would be nice to have as a mid range gun besides the pistol. why would people take the pistol over the musket you ask? reload time and zoom in. The pistol has a clear picture of its surroundings, the musket would have a slight zoom in and blurring of the edge of your vision.

-Changing ships mid game, at the shipwright
Found some friends at sea, or have some coming online just now? Why do you have to change sessions and abandon all your gold/supplies? Go to the shipwright and spawn in a new larger ship for your new, larger crew.

-Rowboat
I saw some suggestions for this, and we can all see that the cover art of SoT has one. There are two (maybe three good implementations that I've seen for this, which i will go into. They would have room four four, as in they have four seats with technically a fifth. One at the back for the rudder, two in the middle for rowing, and one in the front to look like a conquering hero, as your are rowed to shore (jack daniel pose at the front). The fifth seat is for people to solo row the boat by taking both oars. this is just slower than having two people row. Everyone would face forward, but only the front seat would have 360 degree looking capability as the rudder and rowers can only see within a 180 from the front of the boat.

1. They are found at islands, just like normal scattered treasure, but only at beaches/docks.
2. They could be found/sold as small boxes, about the size of the other merchant alliance boxes that allows you to drop it into the water, and then interact with it to spawn a new row boat. I find this one particularly attractive.
3. the Man-o-War i mentioned earlier could have a row boat built into its design as having a heavier ship means you have to park further away from islands to avoid hull damage. The other ships already in game just don't have spaces to store a row boat and still maintain their aesthetic.

-Shovel as a minor stun using the unused Left Trigger function for it
Wielding the shovel, you can pull the left trigger (Xbox controller) to use the back of the shovel's metal bit to do a quick, silly face slap to an enemy that stuns them for a half a second. This would not work again for 10 seconds, to avoid abuse of the stun, the stun would be more for getting away from skeletons and maybe some use in actual combat.

-Dueling others
I would love to pass the time on long jaunts out to sea by dueling my mates. Sharpen that PVP but also pass the time when you just have to go in a straight line for 20 minutes. This could work as an emote similar to the make friends. You would drag your fist across your neck and kinda jerk your head the other way in a throat slash motion. If both players (does not have to be crew) do this within a second or so of each other then a duel would begin. You would see the word duel and the name of your challenger below that, then it would count down from 5. At the end of the count down both players can damage each other, and the duel ends when they leave render range of each other, OR one dies.

-Buying Supplies:
SoT is in dire need of a money sink. One thing that would be great is to have the Merchant Alliance sell you amounts of cannonballs, bananas and planks - 50 25 25 in the same order. The cannonballs could go for 800, the bananas for 400 and the planks for 500. This would give a reason to keep accumulating gold as when you run out of cosmetics to buy, what else is there?

-Cannibal tribe as new enemy
With spears to throw, and poison darts for ranged attacks that deal damage over time (similar to a snake bite) they would have tiki masks and move around closer to the ground with bent backs and knees. They would also have a sword that had sharpened obsidian plates similar to the aztec weapon, Macuahuitl.

-New weapon the Dagger
Even faster than the Rapier, and doing the same damage, but cannot block. Instead of blocking holding the Left Trigger would c**k the dagger back for a throw. with half the distance of a pistol shot before it begins to arc downwards the dagger does 52% damage when thrown and 8 % damage when you slash and has a 5 strike combo.

-New weapon Pike
With a longer reach than any other melee weapon, it is commonly used to keep your distance from other melee combatants. What's special about it? You can hold the charged attack on it indefinitely allowing you to hold your ground, you can even spin your character from this held position to track enemies. it would attack as fast as the cutlass doing 20% damage, and 45% on a charged attack. The reach of the weapon would be about 2.8 times the reach of a cutlass and have no block, so if someone gets close you might not have the best time. best employed in teams to keep enemies at bay, rather than splitting up and attacking.

@lady-aijou Fixed, sorry for the inconvenience.

-Cannon zoom
It would so great if you could get a slight zoom/aim with the cannons. it wouldn't have to be anything too big, just a little to focus on your target.

-Magical Items
Found on islands and in shipwrecks as random loot, these items are one use powers basically. I could think of any number of items from a green crystal that would change the wind to favor your ships direction, a trident that could be struck down into the ground and start fountaining water like a chest of sorrow, a skull coin that once thrown in the sand would summon 6 skeletons that would act as your allies, a snake idol that when placed down produces poisonous clouds in a small area, a seashell horn that would banish your mermaid until you die, a black shark tooth that banishes sharks for a period of time, a chalice that would restore you to full health and giver health regeneration as the same speed as drowning drains your health for a minute. etc etc.

-Drinking Health
When you drink a full cup of grog, you gain health back at 1%/sec for the duration of your stupor. That way it's not a true advantage in combat, but for regenerating small amounts of health out at sea.