Yeah, since the buzz about Mario Kart is it's a trackless darkride, I can say without a doubt Mario Kart will NOT be like Test Track. Trackless darkrides don't reach the speeds that a Test Track type of darkride can reach, but that's totally alright since that's not what they're aiming for.
Trackless darkrides have a smorgasborg of potential, especially with interactivity. That's what Uni is aiming for and I do agree with JungleSkip this'll be the honest to god family attraction we want Universal to have.