More than a GC version I'd love a 5-Door Hot Hatch / Shooting Brake version of the M2. This would make the car so much more practical and a really useful daily driver that is mega fun to drive.
I know it's not gonna happen as BMW isn't in the Hot Hatch segment but the M2 is an excellent platform to build an M2 hot hatch (I'd just personally prefer a 5 door version ala Golf R, Ford Focus RS etc).
I am not sure an M2 GC would work with the current wheel base as the backseat will likely have very low headroom unless a hot hatch design was utilized.