Out of curiosity is this an effort to split the very broad GT1 class? Because I foresee a bloated limited class all the same.
I could put my M3 on a 235/40/18, 200AA tire and destroy any lighter low hp cars that fall into the Enthusiast class. As power to weight isn't a factor but weight to tire is.
A 235 at 3000-4000 pounds puts most factory performance cars that might be in the hands of beginners coming out to drive in the limited class. And then serious performance cars like vipers, vettes camaros could be in the unlimited, punching up against caged cars on slicks big and small.
I don't think many people would be shopping for narrower rim and tire setups to compensate for their lack of HP or limited skill to get into the right run group.
I think 3 classes works for global time attack because they split FWD, AWD, RWD which often dictates lap time because of the relationship to power/grip levels
Plus the majority of the traveling drivers for global have high power FI motors, DTM level aero.