I have heard about the re-theming of Rockin' Rollercoaster as well, although I had heard they were looking at going with a more modern band as Aerosmith is getting a bit out-dated. They have plans to create a kind of "Green Room" where its like you are backstage with the band. Apparently, this was another thing that got put on hold by the recession.
In terms of villains, Jim Hill stated in a recent podcast that he thinks the villains park may be coming back, albeit way down the road. Apparently, the guy that is set to follow Iger came up through the parks. He is supposed to be a very creative type and Hill says he can see where this guy would see the benefit of a villains park. Plus, what better way for this guy to stamp his name in the Disney history books than to open a brand new park that is going to be wildly popular, if it is done correctly. Hill said he thinks it will probably be 20 years down the road, but he thinks it will happen.
And yes there is a ton of room behind Rockin' Rollercoaster. Having run the Disney Marathon twice and the Wine and Dine Half Marathon once, I can attest to the amount of room that is back there. I thought that part was never going to end. There is apparently quite a bit of land around Hollywood Studios that can be developed as well. Not just the backlot portion, but going into the woods that surround it as well. That area is not part of the protected area Disney has set aside never to develop so they can build out if need be. I don't expect that to happen too much, but the point is they have more than enough room.
I agree on the thought of Disney changing if you go too much. My wife and I got engaged and married there and had the annual passes for 5 years. Near the end of that stretch, I was kind of getting to the point where I was ready to do something else because every vacation we took was to Disney. My wife got laid off from her job last year and we had to give up the passes about this time of the year. We have since moved to South Florida and are getting ready to get passes again. After a year away from going, I have found that I miss it, especially since we now have a 2 year old that is deep into just about every Disney Channel cartoon they make. I'm really looking forward to taking him back. We have been one day (on a pass from my sister) and seeing his excitement was great. Its like we are now getting to experience everything new all over again.