Well i made this suggestions on PotBS forums but without any reply so i try here:P
First as i understand that main focus is on ship combat which is great dont forget about "world map". I love idea put real world map with time frame limits of course and possibility of global economy making me shiver:P All aspect of trade between Europe and America could be nice and can bring new aspects to game like treasure conwoy or escorting tasks. Also i like idea of guilds (societies) in game, not sure that you plan make nations into game or some kind of RvR but i love see them as well.
From more minor things could be nice for players make own flags or sail patterns or even clothing disigns for guilds! as we know this from PotBS. Sorry for compare so often to this game but at the moment there is no alternative age of sail mmo title. So i belive its a bit natural, plus many of your future players will be current or ex-potbs players for sure. Another reason is that some aspects from PotBS that may be implemented in Your game as well some bad which need to be avoid (like useless ships, broken group strength, etc)
To keep in topic: (IF) there will be nations on Your game could be nice that they use own historical ships, like english player can use HMS Victory for example and french Le Soleil Royale ! Not sure it is possible but i think that could be interesting for gameplay.
Ill keep fingers crossed for this project and see ya on sea asap!