I just can't see Mario happening in USF.
Considering how low-capacity KidZone is (E.T. being the only attraction an adult without kids might seek out) compared to the 10 acres it covers, why wouldn't Mario come to USF?
Mario Kart E-ticket, Yoshi's Island E-ticket, DK D-ticket, WarioWare/Captain Toad-themed flat rides (both franchises lend themselves well to a wacky flat ride), maybe a Peach attraction (a M&G/show)>>>E.T., Animal Actors, a toddler-only show, two play areas and a kiddie coaster.
It also fits the trend of Universal replacing old, lower-capacity attractions with more relevant, high-capacity attractions:
Transformers replaces Stage 44
Springfield takes over an essentially desolate area of USF
Diagon Alley (2 attractions) replaces Jaws (1 attraction)
Fallon (higher capacity/more visitors per hour) replaces Twister
F&F (same as above) replaces Disaster
Comcast wants to utilize their space as best they can. It fits their theme park model to take a middling kiddie area and replacing it with a family-friendly section on par with the California and Paris Fantasylands (soon to be Tokyo, too)