Jeff Lange has now also posted a quick video showing the Princess Meet & Greet.
http://www.youtube.com/watch?v=F2ztt0R5GyM
MUCH MUCH less themed, it's quite obvious that it's temporary. Also, it appears that this only takes up some of the second theater, perhaps the back half of the seating area. So it's quite possible that all they did was take out some seats, install some temporary flooring to level it out, add some walls, and the theater survives underneath it all.
I could easily see it going back to a theater after the princesses leave. (Now whether they'd put it into Guest use at that point, or just use it for Cast meetings, that's another whole discussion)
-Rob