It's pretty hard to pick just 3 here but:
F,P,T
F (Quest Types) - pretty obvious. There is not enough variety as of now.
P (PVP Bounty System) - I remember reading someones idea about wanted posters being posted at outposts and potentially even having a parrot fly to your ship and drop wanted posters when someone in your server is being overly aggressive to other ships. I think this idea would add incentive to pvp. It could also possibly encourage more interesting interactions.
T (Ghost Ships and Undead World) - Ghost ships sound great but also I think there should be skeleton ships sailing around. Either way, NPC ships should be a thing. It gives us ship to ship comnbat with something besides other players, also adding a new, more interesting way to obtain loot.
I love the game so much and can also see several other ways it could improve so...
Those 3 said, it would be pretty hard to execute T (Ghost/Skeleton Ships), without the addition of H (Map Size and Exploration). The map is too small for a good spread of NPC ships. Also, exploration is kind of uneventful so it could def use some love.
Also, M (Fishing). Everyone wants it. The idea of adding chum buckets that players could potentially fill with raw fish and let sit, becoming chum, would be great. Players could make chum, throw it to the ocean to catch bigger fish (assuming there would be a system for selling fish you catch). Or potential to weaponize chum -- throwing several buckets around your chip as someone tries to board you, drawing in sharks and maybe a feeding frenzy or something.
