My shot-in-the-blue-not-likely theory: There will be four trackless "go-kart" vehicles, each sitting a few people. The ride begins like RSR, except interactive. So you are tracklessly guided through the Mushroom Kingdom, and as you go through you choose interactive elements. For example, you choose the character you want to "represent", such as Mario/Luigi/Peach/Bowser/Toad/Yoshi/etc., and it changes that car's emblem to that character's logo. Then, you reach the point where you race, and here, now YOU take the wheel for a 45-60 second long race segment. It would probably go relatively slow, but fast paced enough to make it exciting. 1-2 riders might drive while 1-2 might manage items, which would be done via screens on the kart. And in order to stop backup, there can be a system where if someone doesn't move their car at all for one reason or another, it is tracklessly guided to the finish line, albeit a bit slower so nobody can just cheat and win while not racing.