M2 + I6 = FAIL
M2 + I4 = WIN
You think BMW is going to give the M2 the engine from the M4? Or you think an OEM tuned N55/N56 is worth an M badge? The N55 is almost as heavy as S65.
If you want I6 just get an M4, if you can't afford M4, but want I6, just get M235i. Let the purists get I4.
If it was only about I6 smoothness, why did BMW give the E9XM a V8? Why did M3 E30 have I4 whereas 325i E30 had I6?
The M2 is about handling, and 328i F30 handles better than 335i F30. If the next M2 gets an I6, it will be the same car as the current/previous E82M: good car but wrong powertrain.
A heavy I6 is inacceptable in a lightweight M2.