If BMW doesn't want to give the M3 "only"/"at least" a NA aspirated engine, it is not becasue they can't, but becasue they don't want. Below the M3 we'll have an M340i sDrive and xDrive. Isn't that a good solution ? NA Motorsport engine for M3 and torque monster "redlight racer" for the M340i !
Again BMW doesn't want. Porsche could with the new 3.4 and 3.8 H6, and AMG als ocould with the new 5.5 V8 in the SLK AMG.
If the M3 gets a V6, it will be a good car. If it gets an I6 (which is not NA) it will be a "bad" M car. I think V6, so still good car.