There is no longer awe associated with breaking records/introducing diverse tech into motorsports anymore. I guess previous generations had it better as they could watch how somebody breaks 190, 200, 210, ... mph barrier, run engines with 900, 1000, 1100hp for the first time, run two sets of rear or front wheels etc. None of that applies now, motorsports are now regulated and consolidated. New revival attempts introduce super ugly cars (look at IndyCars in the past 10 years, or even current Formula E), all mind-blowing racing that deviates from the norm is now banned (Zanardi's "The Pass" can't happen anymore), engines can't be pushed to higher hp unless we want to allow multiple casualties per race, as Firestone Firehawk 600 shown us in 2001 we already crossed the threshold of what humans can withstand and had to backtrack... F1 is now boring (who cares that some German guy in a red car wins?) and mainly a world unto itself with very little connection to the real world as the rules are a result of decades of political fights (i.e. they aren't representing technological pinnacle of what is possible rather what powerful people allowed each other). There were glimmers of interesting things happening with drifting etc. but they never had mainstream potential. I really don't see much future in this, the existing motorsports can be probably milked for a while with a proper marketing strategy, but the future lies elsewhere.
It would be interesting to do remote control. I.e. nobody in the car. Two classes: one with restrictions (i.e. driver must be in control - no assists / etc. May be tricky to define.), one without (want to go fully computer-controlled? Sure!).
Although it would be interesting to go "you must have a space where a person can fit, and if you ever kill the dummy inside you lose the race" (defined a little more precisely, of course).
Remember: you probably want to keep the scale vaguely car-size. That way you'll get the most applicable innovation coming out of it. And also that way it'll tend to be the most interesting to spectators.
