I would love to see a pirate/sailing themed rpg world. "A vast ocean littered with ships and small Islands full of adventure and loot. All to support a world where people can be who they want to be on the open seas. Build a ship, gather your friends, and sail off into the sunset. Fight battles, enjoy trade, and socialize on this oceanic world."
I would imagine people starting factions and they take ships and explore/conquer territory, and have other islands specifically for the mingle and trade of other, more casual players. I would certainly love to have my friends with me, sailing and gathering resources on the small islands scattered about. we would certainly have an island to call home, with a beautiful harbor that anybody could stop by and stay, sort of like a hotel.