As a 2016 WRX owner I'd be totally disappointed if the BRZ had the WRX engine/turbo... You are directly connected to the engine with the BRZ. The WRX is nice but its acceleration feels artificial and is only fun when the turbo kicks in.
Plus, other than in a straight line, the BRZ can be just as fast or faster than the WRX. I'm fairly certain that if you live in the mountains with lots of twists you'll drive much faster and have much more fun with the BRZ
