Actually, even for the BRZ a thick 30 grade like German Castrol or a 40 grade oil is not needed with stock internals.
For someone considering a thicker oil, you should first do a used oil analysis to determine if you need a thicker oil. Even if I had an Impreza that burned oil using 0W-20, I would switch to a 5W-20 before trying a 30 grade. 5W-20's are more stable and usually have better NOACK volatility ratings (less evaporation).
I don't see many BRZ uoa's but there are a lot of good ones on ft86club.com using 0W-20.