A bi-turbo S65 variant will be marvelous!
1. A progressive iteration of one of the best engines ever.
2. Imagine the fun aftermarket tuners can have with this engine!
The second option would be shoe-horning the M5/X6M/X5M engine in the m3...what a freakin beast! It would need wider tires and better breaks but I think BMW is heading in that direction anyways. I wonder if they would offer an AWD system if such an engine were to be made available??? If one were to consider the AWD rumors for the new M5, this engine/tranny option could be viable for the m3 as well.