Going back a few posts, I have to disagree with you guys saying that we can't have a 125 two-stroke against a 125 four-stroke. My approach is that there's no point in trying to make the two fair. It'd be like trying to make steam engines and diesel engines have a fair economic footing by deciding how much free money to give to steam operators. If you stop the flow of handicap money, the steamers wouldn't be able to compete. It would be unfair. But you know what? That doesn't really matter. Morally and logically, all engines should be put on an equal footing to compete, whether economically on the rails or through rules on the track. If someone comes onto the MX scene with a Wankel rotary engine and wipes out all the two-strokes at equal-displacement, that'll suck for us, but we will have been beaten fair and square. There is a big difference between fair rules and fair results. Fair rules lead to relentless competition to bring better and better products. Fair results means relentless pushing to convince Big Brother that the Other Guy's bike is too good.
As I've said elsewhere, I think it should break down this way.
125 Class: Any naturally-aspirated, single-cylinder internal combustion engine less than or equal to 125cc displacement, must homologate.
250 Class: Any naturally-aspirated, single-cylinder internal combustion engine greater than 125cc and less than or equal to 250cc displacement, must homologate.
500 Class: Any naturally-aspirated, single-cylinder internal combustion engine greater than 250cc and less than or equal to 500cc displacement, must homologate.
Open Class: Run what ya brung. Any displacement, any engine type, any number of cylinders. Jets, electrics, turbocharged, Buick V-8s, whatever you think will work. No traction control, no homologation.
The Open Class would be incredible. You'd have a massive search to find the ultimate go-fast holy grail. DI two-stroke? Turbocharged rotary? Stroked 426 Hemi? Who knows?! It would be battled out on the track in lap times and hospital rooms. Anything too crazy would hurt lap times and maybe lead to bad press (if the bike blows the rider into goo, for example) so they'd be cautious to make 8500hp bikes. It would bring motocross back into the spotlight as a properly innovative and cutting-edge sport. I think the technology might be able to exceed F1. And with the other classes, homologation would be set on a factor other than raw numbers, so that smaller manufacturers could participate. Perhaps old NASCAR style, with a bike or two per dealership required production, although that'd have to be adjusted with internet sales.