FE13 originally being planned to take place on Mars and an old thread about an African-themed FE got me thinking about possible themes other than medieval-fantasy.
Personally, I think a pirate-themed FE could be pretty cool. While there have been ship battles in previous FE games, having a large chunk of the game devoted to them could prompt IS to do more with them(ships moving during battles, firing cannons, fighting during storms...). Sailing to different locations would also allow for lots of unique environments.
So what do you guys think about the possibility of future FEs having different themes, and what themes would you like to see?