I know this suggestion might be more effort than it could be worth, but I also think it would be really cool to see something like this implemented.
The only thing you can do with instruments is select one of the available shanties and hold one button to play it. It's practical for what it is, but what if we were allowed to select a "free play" shanty option, hold down (or toggle) the play button, and then press other buttons to play individual notes? A bit like the Ocarina in the old N64 Zelda games. That would allow people to create their own songs on their favorite instrument and play it at will, adding a lot of creativity with the community.
Granted, this option would make it very hard or impossible to move while you're playing, but if you're standing still while waiting for something to cook or for the ship to arrive at its destination, fiddling around with an instrument and creating new songs on the fly could be a lot of fun!
