USH was never master planned to be a theme park. As for Fallon coming to USH in the Shrek 4D space? It fits the space sure but I wouldn't hold my breath. If it were going in that space I would expect the New York façades to be removed in favor of 30 Rockefeller Plaza which would probably fit better with Universal Boulevard's 1930s Art Deco theme. That being said, it's pretty unlikely it is Fallon. Expect no major exterior changes outside of a marquee change and a slight repaint.