The current building cannot really fit any sort of coaster except a wild mouse. Strictly the launch on RnRC, for example, would go beyond the current building all the way to Gringotts. And that’s a single coaster. Duel track is right out.
While they could, in theory, build a second story, it would require removing a lot of the infrastructure for the ride itself.
Personally, if they’re going to change the ride system but keep it F&F, they’re best (maybe only) solution would be the Mario Kart tech, only without the AR element.
4 person cars. Multiple video tunnels with practical transitions. If you want to give it a light interactive element, each rider gets a steering wheel with trigger transmission they they have to time correctly or the gears grind, effecting your time.
It would be much smaller than the current experience, but it could be more fun.