I have a small yet powerful idea.
Officer training. Only one style of play can be active at any time, would cost gold (x per officer) and a week to train (stops people for jumping styles on the fly, forces game style strategy)
1. The way of the Merchant - Ship travel x% faster +x% to cargo hold
2. Pirates Life - Ships have x% bonus attack +x% to plunder
3. Privateer for Hire- Ships travel x% faster, have x% bonus attack
I figured most would be either merchant or pirate, and privateer would be a blended role without the $$ perks of either (what we consider normal $$ now, maybe their $$ perk is being subsidized by nation they protect)