Disney will definitely build a third gate sooner or later. That's why they purchased the strawberry field (Toy Story Parking lot). It's in the Anaheim Resort Master Plan. Key question is WHEN. Considering there's almost never an off season the the DLR now and BOTH parks are always packed, it'll be in their best interest to add a few more E Tickets to both parks, and then start on the third park.
I wouldn't mind seeing more Star Wars in Tomorrowland AS LONG AS it wasn't the ONLY new thing. Throw in Tron, Marvel, an original time traveling ride, and theme the land around a futuristic city to tie everything together, and you're set! Just no single theme, especially one that would destroy an existing classic land. Single Franchise Lands can be a hit (cars, potter), but it's EXTREMELY limiting for future expansion.