Why not just follow ROAR rules?
17.5 is stock, 13.5 is super stock, anything higher is modified, then go have fun racing whatever class your interested in and have a shot at winning (because winning is really fun).
don't worry about speed control technology. Even if a 13.5 is a fast as a modified on one track, it will be just as fast as 13.5's on a bigger track. Some small tracks a 17.5 will be just as fast as 13.5 and modified class. That is totally track dependent. Smart racers will choose the right motor speed (or speed control settings) for the track conditions.
If you want on-road touring car racing to grow in popularity, your totally looking in the wrong place. Go back outside to publicly exposed parking lot racing and offer novice classes (run-what-you-brung) and gearbox classes for off-road cars.