The rumor going around is that BMW is looking at reducing the cylinder count on their M models. Apparently the information comes straight from BMW higher executives, including the CEO Norbert Reithofer, and himself mentioned to Auto Motor und Sport that he would like to see the next M cars with fewer cylinders. But in order to keep the performance up, BMW will need to make their cars "slimmer"(hint: more carbon parts).
Mr. Reithofer mentiones that BMW's new twin-turbocharged inline-six found in the 135i, 335i and 535i, is a good indication of what the future might hold. We already know from the test drives that BMW 135i offers amazing performance, close to the new M, while its price is about $30,000 cheaper.
We're assuming that the emissions standards increasing across the globe are one of the reasons why BMW would go that route. Also, another rumor going around is that in the near future the US government will regulate the MPG standards.