I agree, who really cares what engine it has in it. If they're going to drop weight, beef the suspension, and put a light-weight I-4 in it, it's going to be a track monster. It'll probably be more of a purist, tracker than the M3/M4 which will undoubtedly be heavier, more luxurious and more about straight line.
I bet you this car will be extremely fun, and maybe not very practical. This would be like a Cayman S/R, likely somebody's weekend/track car not DD.
2014 335i RWD: ZMM, ZDA, ZDH, ZPP, ZTP, 2NH, 2TB, 5DL; Z4A MPPK; AW ext / VB int
2014 ML350: P01, R33, 297, 319, 846, 864, 889, 996; LB ext / AB int