Which is something that is happening awfully fast at USF after Fallon, F&F and Nintendo. Sure they still have Fear Factor and can probably add something in Hollywood, but where else can something of any decent size go after these next big expansions/additions without replacing things? Going into the TM parking lot is a slight possibility, but eventually they will run out of land. I suppose that the concert yard is a potential expansion area as well if the park gets to that point, but I have to think Uni would hate to lose that Stage.
IOa still has a lot of space to be renovated to either be brought up to date or be changed to something better (along with a few expansion pads), however again, once everything is filled, there's only so much you can do with two parks that are packed with attractions. A Third park will eventually be needed.