It is clear that there are a few people out there that live and breathe for the M Division Bimmers, and pretty much any other vehicle is not worth it.
I am willing to bet that these are the people that want an M variant of the BMW i8 so badly, that they started a rumor.
Unfortunately for them, BMW official stepped up and denied all such rumors, both for now and for the future. And if you think about it a bit, you will come to the same conclusion. The i brand was never meant to break performance boundaries, but rather to provide eco friendly, premium cars for the discerning customer.
It is true that the BMW i8 is called a sportscar, but this is more about the way it is constructed and how it drives rather than the power it develops. So for those that still wait for the BMW i8M, it is in vain. My advice is to seek solace in the fact that a lot of technology developed for the i cars will find their way on M models (i.e. CFRP).