I've been wondering about the Ferrari FXX program though as sort of an in-between - cars using tech banned by F1 and not road legal in pursuit of new performance achievements.
One hypercar I found extremely appealing was the Jaguar CX-75 using a turbine powerplant. Those are banned in every racing series. The potential though is staggering, mating the best of electric motors and potential powerband efficiency. Drool. Sorry.