Again I'm no insider, but they could use the Studio Tour plaza area, that's a solid 8 acres. They could replace WaterWorld which is a good 4 acres. If they did decide to ever build a 2nd park I've been saying for a while that the Falls lake area would be perfect since it's about 40 acres.
There's always the potential of removing more sound stages on the lower lot. So lots of possibilities, it's exciting.