Speaking with CarAdvice today, BMW spokesperson Piers Scott said that it “it is not clear at this stage, but the sedan may arrive before coupe”. It would make sense, given the 2012 3 Series sedan has just been revealed, while the coupe version, which will probably be named the 4 Series, will be launched later on.
The engine, which will probably be a turbo-charged six-cylinder, will undoubtedly be mated to a seven-speed dual-clutch transmission or a six-speed manual and will slot into both sedan and coupe offerings. Power is expected to be around 335kW, comfortably outgunning the current 309kW V8.

Our spy photographers have caught the M3 Sedan in late testing phase, so it should be mid-next year that we get details on what the M3 holds. Like previous M cars, we may see a concept version a short time before production is announced.
CarAdvice will keep you updated as more information comes to hand.