I'd love to have the option, of a crew system. Where you create a 'Crew' by naming your ship, and making your own logo which you can then buy later on for your ships sails, side of the ship etc. The captain (Owner of the ship/crew) can chose the tax, or simply have a default tax or something set up so your ship/crew can raise money for said purchased.
They have stuff like this in all sorts of games, and I feel it'd be absolutely perfect for this type of environment, and would create a lot of interesting tails for others to experience.
Even have a Crew leveling system like gold hoarder, etc. The rank you are in the crew, you have the ability to change it to your title, as well as level up the crews level to unlock stuff. For example, you have to do missions with at least one other person in your crew with you to gain exp doing anything from voyages to hitting/destroying ships to killing other crews. Once you get level 5 you'd unlock the ability to create your own emblem/logo/etc. level 10 you have the ability to buy sails, 15 or 20 you'd have the ability to use your ships colors. Background color of the logo/emblem will be the main ship color, Background design will be the ships design, and then the logo on the side of the ship.
It would create a huge opportunity for more customization, and increase the playtime on the already long playtime of the game.
For example, Image if your ship was called "Generic Name" and you were the best at destroying, pillaging, etc. other ships, and crews. People would begin to recognize your ships sails, look, style, and name, and begin to fear you. Like "ohh c**p! It's Generic Name! We have to go"
As for if 2 people from a crew and 2 people from another crew somehow join a game at the same time, I recommend the highest crew leveled crew have priority with the ship customization of the sails, and the other crew gets the customization of the ship body. This way both parties have equal showcasing of their ship and can work well with one another. As well as help promote others to gain their crew's level up.
As for the emblem editor I was thinking something like this: