Would be cool to see World Showcase get an expansion, especially since the right side is fairly barren in terms of attractions.
Also, since the UK wasn't ruled out as a proposed area of expansion (Japan and Canada were), I'm inclined to think there might be a Mary Poppins proposal of some sort - especially with the sequel slated for 2018.
France (Ratatouille clone, Impressions de France update)
United Kingdom (stage show, Mary Poppins - first-of-its-kind 'carousel' dark ride)
If only Future World weren't in such bad shape
but two 2,000-2,500/hr dark rides in WS would definitely help Frozen Ever After (and also Soarin'/Test Track, to a lesser extent).