Spelljammer, except with actual water and actual boats and none of that space stuff.
A nautical based campaign world sound interesting and I'd love to read about it.
Solid and well done nautical rules that you could export would be useful for almost any campaign world. Heck you could even use them in Darksun.
Super not interested in yet another euro inspired middle ages-esque castles with armored knights fighting dragons/whatever world. If I wanted Dragonlance, Birthright, or Greyhawk, I'd just use the forgotten realm setting (yes, I went right out there and said it, you don't have to agree, but its my opinion).
I'm also not interested in something *weird* like Spelljammer or Planescape. Weird stuff is neat to read but next to impossible to make it seem consistent. Games fall to pieces when they don't feel consistent. Darksun is good because it is a desert world with dictators. Cause and effect is common sense in the world. Run out of water in Darksun? You don't feel good until you die or find more water. Nothing to explain, and nothing that will cause players new to the setting to sit there and not do anything because it isn't obvious how the world works.
Ravenloft might work, but it would need to have rules for running 'low power' campaigns (and I don't mean swingy oops your dead mechanics), investigation, and running away. Four encounters a day where you beat up werewolves wouldn't be Ravenloft, and I can already do that with the current rules. If they gave me rules and advice for running 4 encounters with the same werewolf without making it feel like GM fiat, then that would be useful.