Machta: 5th gate = new park. Eventually, some day, most likely, it'll happen. I think we're at least 5 years or so away from Disney even looking at DESIGNING a new park, but we'll see. The increase in numbers for WDW, if sustained over the next few years, may fast track that.
ChuckS: I agree. It looks like the new "Pixar" area in MGM is going forward, with the Midway Mania ride being the first cog in the machine. But MGM is somewhat limited in area it can expand into. From the rumors, it looks like the Backlot may be history, and the Pixar area will take over much of that land (and some cast parking and outbuilding areas, too). Once that's done (2 years or so)...I think MGM is probably mostly done. AK is going to be a big question mark. Everest is doing a good job of pulling in guest but I agree...they could use more D and E ticket "ride type" attractions. Maybe, someday, we'll get Beastly Kingdom over there....or something else to balance out the park a bit. Again, though, I think with the sheer numbers Disney is seeing, that will likely happen after, or toward the end of, The Studios project. I wouldn't be surprise to hear it's in the planning stages soon, actually. And yes, Epcot (and by them MK) will likely need some freshening up. But that will happen in the normal course of things, as it often has.
So that puts us ABOUT 7 years out from now...2014-ish. AK opened in 1998 (hard to believe it's been almost 10 years!). I'd expect we'll see SOMETHING in the way of a 5th gate by then.
JimC: Many of the reports have indicated it wasn't so much the $$$, but the demands Jo Rowling made from Disney. Demands that, apparently, were significantly lessened (if you look at the scope of what Universal has put out there, and the plans/picture) for Universal. Why that is, or what exactly happened during negotiations...I guess we'll always have to wonder. But I'm not sure Disney dropped the ball on this one, entirely. It'll be interesting to see what they do in response...because you KNOW they'll do something. Maybe it's the Pixar addition to MGM....but I wouldn't be surprised to see something "larger" announced within the next 6 months or so.