If I am not mistaken, wasn't more going to be added originally when the ride's were in development for USH and UOR, that would've included more elements? I may be wrong about that, but I believe if I am not mistaken; that GE basically screwed them over; especially USH's.
That said, I think Mummy has been said that it may close not due to popularity, but on the ride system in-place. I may be wrong about that, but I thought that is the case.