Originally Posted by doc19
I believe the reasoning is the power domes in the e46 and e9x were purely a matter of being unable to fit the engine under the current hood. I recall watching a special on BMW and they specifically discussed how the M division went back to the powers that be and asked if they could add in the dome to accommodate the v8 - suggesting it wouldn't be there otherwise. If you look back at the e30 and e36, there was no dome.
As this car appears to be roughly the same dimensions of the e9x I would assume they would be able to fit either an inline 6 or a v6 under the hood without modification to the exterior. This is just my assumption.
As far as I've read, the dome (at least in the case of the E9x M3) was to help cool the V8. I think it would fit without it, but it would overheat without the room above it for air to flow over. I doubt a six cylinder turbo would need a power dome, look at the F10 M5 which has no power dome.