For a Mario Kart ride, I really think the idea someone else had pages ago(sorry, not going to hunt for the post, but feel free to chime in) where it would be similar to the Simpsons ride really may be the best idea. Have a large number of kart ride vehicles that fit a few people each, maybe like 6, and have them on their own motion base in a large dome screen. The individual karts could go up, down, spin, shake and do whatever. It would replicate the game experience fairly well imo.
The biggest hurdle to that is that the simpsons ride would be virtually next door. But, that could be worked around if they wanted to scrap the simpsons ride for a Simpsons "phase 2" with a dark ride tour of the nuke plant or whatever. Might even allow for better use of the land/MIB plot. Of course thats a lot of work just to basically replicate a ride. Not sure if its practical.