Currently, we only have 3 real ships - The Schooner, the Brigantine, and the Galleon, and aside from being direct upgrades they all fill in a similar middle-ground roll. It'd be nice to see some more variety in the types of ships we can build, as well as seeing them lean more towards one role rather than the middle ground, similar to the following breakdown:
Cargo:
Xebec
Snow
Fluyt
Galleon
Speed:
Pinnace
Caravel
Clipper
Combat:
Frigate
Third Rate SOL
Second Rate SOL
First Rate SOL
Jack-of-all-trades:
Schooner
Brigantine
Brig