Plus you really don't close down a whole land to place one ride. They removed the whole land to replace it with a whole new land. The odds of it not being a HP expansion are really slim. People flooded Universal when they opened the first "phase" of HP and they will do the same again whenever the next phase happens.
IMO, Universal is going to time the opening around the time that the Avatar area opens at Disney's AK and they are really smart for doing it that way. More people would visit Universal to see HP than they would do see Avatar and Universal likes to draw the attention away from Disney as much as they can.
As far as Transformers go, I really could see Universal holding off on bringing it to Olrando. When (its only a matter of time before it happens) Universal loses the theme park rights to Marvel, they have a ride concept in their back pocket to toss into Spiderman. Since they use the same ride system, it would not require a ton of work to turn Spiderman into Transformers.