The "royal edition M3" has officially been revealed by BMW as an "April fool's joke" so I would not be surprised if this is an april fool's joke as well.
If it were true, I applaud the usage of the E90 sedan over the coupe since M3 sedan with a b-pillar would make a much more rigid chassis for a track-oriented M3. Plus the sedan has advantage of being 3 inches shorter and a bit wider. More lateral grip and less weight of the overhangs.
""A great sounding, responsive, high-revving, naturally aspirated engine is part of the DNA of a thoroughbred sports car. No two ways about it."
- Lamborghini on turbocharging