I dont' think MK needs an E-ticket ride in the near future, even though I hate to see the old 20K site go to waste. The MK is easily the biggest draw at WDW, so if they don't change anything people will keep coming. I personally think the just need to reveamp a few of the older attractions: Space Mountain, PoTC, HM, and the Jungle Cruise.
MGM probably needs one the most, it's still my favorite park. They need an E-ticket ride to draw the crowds away from Sunset Boulevard. Star Tours is getting out dated, they could easily change the video to make that better. I dont' really want to see an Indy ride, unless it is original and not just like DL and TDS.
Epcot doesn't need anything right now, they've got Mission: Space and Soarin' in the past 3 years. They do need to do something with the Wonders of Life Pavillion and Universe of Energy. UoF takes up such a huge space, yet such a crappy ride is in it. Maybe they could add a ride to the World Showcase.
AK probably won't get it because Disney just poured a ton of money into EE. They do however need a ride near Camp Minnie MIckey. They need to do something to Dino-rama, that place is just a piece of crap. I dont' care if the imagineers wanted it to look like a carnival, that stuff just doesn't belong at WDW.
ACtually I dont' really care where the next ride is added, I just want an original ride that is not a clone, not to mention a large budget.
That's just my two cents.