Unfortunatly, not too much is known about the car beyond the fact that the basic shape will be along the lines of the E90 (with details dovetailing with the new BMW styling ie. F10 and F12), a GT may be introduced into the 3-Series family and expect some downmarket/efficiency features such as 3-cylinder and 4-cylinder engines.
Heres the best full list of articles relating to what we know about the F30 so far:
http://www.bimmerpost.com/3-series/f30/