I would be shocked if any form of the new M3/M4 comes out in 2013 calendar year. If there is one it will be the sedan in late 2013 but my guess would be early 2014 possible still being a 2014 "model year" I wouldn't expect the coupe until early 2015.
If I remember correctly 2 generations ago started as a 2001 model, then 2008 model for last generation so that means 2015 for new generation... And the 2008 model was actually early 2008 calendar year release. So we could be 3 years away from the next M3! BMW really sticks to the 7 year cycle thing.