An M3 is an M3. You can't spend 30 years building such a name, pure benchmark for every single automaker out there and all of the sudden change it to M4 because it's a new naming system. What would be interesting is for the M3 since it's such a name, such a car and such a legacy, to be the only one not to follow the new naming system. The M3 has always been above all else. This would be no different.
But the new "M3" being a Sedan, turbocharged, I6, with no screaming 8k redline, makes you wonder if it's an M3 at all.
Now, all the comments of "c63 here I come", "My next car is a p-car", etc, are non sense. I would never stop buying a car because the badge has a different number on it.