Every park needs help and fixes in areas, even brand new ones (those sometimes need the most). USF, despite misfires and some old things, is actually in pretty good shape all things considered. This year Bourne, F&F, Fallon, Gringotts, HE, Diagon, FFB, Transformers, and Minions are all under 10 years old. Of the attractions offered at the park the following don't pull their weight, IMHO: Shrek, F&F, Barney, FFL, Animal Actors.
So my vote goes to Fear Factor Live. As a show it's pretty bare bones so could be updated and it's in the back of the park so a late morning to evening new stunt show would be perfect for this location. Since Bourne is going to be more "in universe" it'd be cool to see this stunt show be like a modern Indiana Jones just way shorter while still having the "making of" aspects.