Unlikely, but not entirely impossible.
The current generation BMW M5 and M6 are wonderful high-performance machines, but many M brand purists aren't satisfied with either. The 6 Series is, more or less, a coupe/convertible version of the 5 Series. Same deal for the M5 and M6. They share the same 4.4-liter twin-turbo V8 and gearbox, amongst many other things. The previous generations, however, were powered by a naturally aspirated 5.0-liter V10. People rightly miss that and some enthusiasts consider the new powertrain setup too tame for an M car.
They may be right, and BMW's M division listens to its loyal customers. There's currently a rumor going around that originated on the BimmerPost forum stating that BMW hasn't ruled out a return to the V10 for the currently in development next-generation M5 and M6. Yes, we know that sounds very unlikely mainly because the entire industry is in the midst of downsizing due to increased fuel economy regulations. In fact, BMW is partially leading the way with its dedication to turbocharging. Just look at the new M3 and M4 as further proof. So the thought of a new V10 sounds great, but in reality doesn't seem logical. But you never know. BMW does want its customers to be happy.