Let me straighten things out for those of you who are confused:
You know how we have the 5-series and the 6-series now. BMW wanted to separate the 3-series sedans and coupes into the 3-series (sedans) and the 4-series (coupes). So there would be no 3-series coupe, only 4-series coupe. You turn the coupe into an M car, you have M4.
But, BMW decided NOT to use this system. The new 3-series will be coupes, sedans, and convertibles. So the next 3-series M coupe will still be the M3.