The Speedway takes up about 4 acres. I think Martin is right on this one though, Disney is spending bookoo bucks on the TRON ride with it's large attention-grabbing light-show-having canopy. To then turn around and block it from an entire cardinal direction with something would be a surprise. It's far more likely that the Speedway gets chewed into bit by bit for other things until it's one loop.
I think the best use of the speedway is a smaller, windier two-lane car ride. Something more reminiscent of a drive in the country (like Autopia at DLR) than the current NASCAR-style grand prix. I always liked the Tin Lizzy at a lot of parks (including one in my hometown). To see Disney do something like that with modern electric cars would be nice.