Have you not been paying attention? The 2012+ Impreza is lighter and the BRZ is relatively light. Subaru has stated that they learned a lot from the development of the BRZ that will be incorporated into the next WRX/STI. One obvious carryover has been Subaru's own direct-injection technology in the new Legacy and now Forester turbo models.
I wouldn't worry about them not being lighter. The biggest question for a lot of people right now is, "Will they make it smaller to compete in WRC?"
Anyways, I just wanted to share the Forester news because it's cool to see 250HP and 258TQ on a 2.0 while only being mated to a CVT. It makes the next WRX/STI look that much more promising.
Also notice that the Forester non-turbo finally gets a 6-speed manual. Subaru is listening!