They simply need to ask users one question. Are you using a touchscreen OR are you using a mouse? If you have a mouse, present them with a Win7-like interface without any of the touch stuff that involves using the corners of the screen or popping in and out of a fullscreen start menu.
Watching people do coding demos at BUILD, you never saw them use any of that stuff because they figured out all the keyboard shortcuts. Once in a while you would see the fullscreen start menu pop up for about a half a second and it was quite jarring.
I just hope Microsoft doesn't ruin a perfectly good modern OS because of misguided business reasons and plain old stubbornness. I'm far more interested in WP8 than Win8 because on a phone, all of this stuff is great.