Don't be surprised if it ends up happening.
Yes, the all-new BMW M3 and M4 have just arrived, but that won't do anything to put the rumor mill to rest regarding their eventual successors. As we all know, BMW, like all other major automakers, is in the process of downsizing its engines in order to comply with more strict fuel emissions regulations. The naturally aspirated V8 from the previous M3 has been replaced by a twin-turbo inline-six. Power is up and emissions are down. It's a win-win for BMW.
So successful is this formula, there's reportedly a chance BMW will go a step further when it comes to the next-gen M3/M4. Australian publication Motoring claims that BMW M Division Head of Product Management, Carsten Pries, said it was "foreseeable" that a four-cylinder engine could be used in the next M cars. For sure you could see a future (M3) powered by a four-cylinder engine," Pries confirmed. Another reason for an even smaller engine is weight. "Performance can be boosted with more power, but if we are to address issues like emissions and consumption, we have to look more at weight. We decided in this generation to address the (upward) weight spiral."
Again, it's very premature to draw any conclusions, but downsizing and turbocharging is very much here to stay. High-performance divisions such as M will do what is necessary to guarantee power is up while weight and emissions are as low as possible. Hey, at least they're not talking about a hybrid M3 (yet).