Here's the problem with that:
We already have a speed limit on the course. The jet class is coming up on it with aircraft that don't come anywhere near the fastest of this era. If they were to allow swept wings and afterburners, they'd be capable exceeding the speed limit with 50 year old machines. And this doesn't even account for the fact that we're probably not very far from unmanned aircraft that would be capable of running the course supersonic.
Once the technology exceeds what the venue can support (or what the human pilot can support), it changes the nature of the sport. Instead of racing as fast as you can, it becomes an exercise in who can get the closest to the established limits without exceeding them.
There's nothing wrong with this. Bracket racing in autos is hugely popular, but it doesn't do anything for me. I'm also not a big fan of Nascar. I'm pretty sure that Formula 1 (auto racing) tried for years to ban traction control technology, but eventually gave up, because they just couldn't prevent cheating because it was too easy to hide the technology. It probably made for some interesting drama, but it's just not what I am looking for with racing.
I'm not sure that I could justify why I feel the way that I do. I have no problem with defining parameters like airframe powerplant design that must be met, but without any restrictions beyond the physical parameters. I love the sport class. But once you start artificially slowing things down with fuel flow restrictions and the like, then I start to lose interest. And that would inevitably happen with turbine or electric power plants.
Frankly, I think that the sport class as it currently exists is the best thing that's happened to air racing at Reno in the entire time that I've been going.
Where I do agree with one of the points of this thread, is that (unfortunately) there doesn't seem to be a lot of future in the current unlimited class. The equipment is just getting too rare and valuable for it to be viable.