odds of a new engine are about 0.0%
odds of electronic gadgets, radio, etc changing 100%
the car was just redesigned, they just redesigned the Forester, and are working on the WRX/STI redesign/relaunch (no longer Impreza's, mind you) and then probably the Outback before they work around to making big changes to the 'new' Impreza.
All opinion, of course. But if they introduce a diesel or turbo Impreza in the US before 2016, come back at me and brag about how wrong I am, lol.