As a BMW fan I know M division will come up with some crazy awesome engine for the M3. No doubt about it. The M3 is the icon for the M division and I bet it will surprise us all with something no one here has imagined.
As for weight issues, lets not forget the S65 V8 is lighter than the previous I6, so I don't think they will go back to I6 after blowing everyone's minds when they changed to V8 in the E9X. It makes more sense to turbocharge a V8 to get figures that match future competition since everyday we get more powerful engines for the same models.
Lets not forget this engine will enter the market in 3 years and will be in the market for another couple of years, it's for THE M3, and has to be turbocharged.
BUT I want to get an E92 before they're gone just to keep the last M3 NA engine with me forever.