I don't really care about pirates as such but a game with actual involved wind and sail mechanics is what i want. Sid Meier's Pirates! was cool because it did actually incorporate wind and the rig wasn't just there for aesthetics. Ass Creeds naval combat looked cool but was far too simplified.
Honestly, Sid Meier's did pretty much everything right, it's just that nothing it did was overly complex, the game didn't have a whole lot of depth. Flesh the world out a bit more, expand the cities, make them more unique and not carbon-copies of each other with slightly modified numbers, make the political relations between the various factions/pirates etc more intricate, create a more in-depth economy, deeper crew/fleet management. Basically re-make Sid Meier's, do everything that did but expanded upon and i'll be happy.