Well you can say that, but what AWD modern turbocharged car gets better mileage?
When you boost a 4 banger on AWD, you are looking at about 19-21 mpg in pure city, stop and go from light to light.
If you want 30% better, then something drastic has to change. Less weight is the biggest improvement.
I do not see the next golf R making much better mpg. However, I think the next impreza could easily get 20% better if it is lighter and has Direct Injection. But then you can bet you will get another 265 HP car. You may see 280 with marginally better mpg. It is a balancing act with no secret formula.