Truthfully, I wouldn't be surprised if Disney re-theming Test Track to Cars. I don't want to be negative on this or anything, but I really wouldn't like to see them do this. Though Cars Land's Radiator Springs Racers is the same same ride system and all, if they brought this to WDW, it would not fit the theme of Epcot at all. And dedicating a Future World pavilion to Cars? Hmmm....
I'm one of those who really doesn't mind The Seas with Nemo and Friends(even if it "ruins the classic pavilion", as I've heard many say). Bringing more current Disney/Pixar characters to classic attractions isn't always a bad thing. For Nemo and Friends pavilion, I don't mind it(even thought the OmniMover ride isn't all that great). But for Cars to come to Test Track, I'm wouldn't be a fan of that.