Hm, this isn't completely related
But it gave me an idea.
Since Windows 8 has an ARM build, maybe they could add parts of the ARM build into the AMD64 mainline build - and allow the AMD64 CPU go into complete shutdown in idle periods. Obviously a machine is never entirely idle, and that's when you use the WOA code running on an ARM chip to keep the GUI updated, and so on, until x86 code was required, or anything heavy computationally.
I'm sure somebody at Microsoft is thinking about this.