Personally, I'd love to see a pavillion that represents the great nation of Fraggle Rock.
But in all seriousness, something (and I'm stopping just short at saying anything) needs to be done in World Showcase. It's starting to get boring and the crowds that I see back there when I go are starting to show it. I never have to wait for Maelstrom anymore, and the shows I see are playing to half capacity or less. The only time I ever see it moderately crowded is around dinnertime and for Illuminations. Maybe this Kim Possible program that they're running now will help pick up interest, but I can't see much past young preteens and their families.
Personally, I think both renovation and new pavillions would be a good idea to boost crowds. The E-ticket in Japan that's been tossed about for years could be the best part of a solution, plus more rides in the relatively empty pavillions (I'm looking at you, Equitorial Africa). Then they should start thinking about new pavillions: Russia, Spain, Australia, Brazil, Greece, and Israel have all been tossed around since Epcot opened. Any one of them could bring in more people (though I wouldn't recommend using Israel for a while. There's just too much controversy there) and would be able to keep people in Epcot for a full day.
(Though in all honesty, I'm a Future World boy myself.)