Generally, I'm an autocrosser with SCCA. BUT, I WAS building a stocker pickup for IHRA when they killed it all. All this discussion is interesting, but maybe you could gain a different perspective by looking at how SCCA runs it's autocross program, from classing to rulemaking processes. The rulebook is online at
https://www.scca.com/pages/solo-cars-and-rules so you don't have to spend a penny. Its a club---for the members. I think this forum should consider looking for a different organizational model for their interest.
Oh, and by the way, SCCA has a 30 year rule for the Street class. Don't think NHRA can't/won't insert a year rule, especially if the older car people start making trouble with NHRA. The SCCA 30 year rule is in place to remove the "unicorn" car to have from dominating a class.
Oh, yes, SCCA has TOO MANY CLASSES, but far fewer than NHRA. 1400 autocrossers in a weeklong nationals (2 days per class) and almost nobody torn down. a few contingencies, no purse, but a pretty exclusive jacket for winning a national championship...