Dont make the mistake of thinking that V8 Supercars have plenty of freedom in the rules. Revs, weight, compression, suspension components, a horribly small control tyre. Limited aero etc etc all mean that given a clean sheet of paper a team could make the cars go far quicker. Keep in mind that at some track Carrera Cup cars are as quick-quicker then the Supercars.
They are still race cars, but free up some of the rules and the teams could make the cars lighter, bigger tyre, better aero and more power.
But would be interesting....like any form of tin-top motorsport, any car with a technical advantage will be hobbled to allow for other makes to compete.