Yeah a M3, M5, M6 is not a supercar and never will be one. You can throw $$$$$ into a Honda and make it compete with a supercar but even at the end of the race your still driving a modded commuter car or even sports car. I could care less if a Honda beat me and I was in a Porsche GT, because even if you lost the race your still driving a crazy cool expensive car.
I consider a Lamborghini Gallardo a exotic, but an aventador a supercar. There's a fine line that most people wouldn't know the difference.
Also, many people think just because the car is an exotic makes it a supercar, but it's a car by car thing. It has to be exotic but also have the power and speed to throw it into that higher level like a s7, Bugatti, porche gt, Enzo, and venom gt have. Usually the price reflects the status also, 200k and under and you can get a beautiful exotic, but a supercar to me is usually over 500k. That being said, there is no way on gods green earth that any BMW M series, current or previous will ever be supercar status, unless they come out with something new.