My wife and I discussed this a couple of times and thought it would be amazing if you could create worlds based upon the tracks of Mario Kart 64, with all of the shells, banana peels, mushrooms, etc. It would obviously need to be something that individual, small groups could ride on, because having 1800 riders all throwing red shells around would make for a pretty miserable activity. But seriously, it would incredibly fun for smaller groups if it would be feasible.
nick