The rumor mill seems to indicate that it would be optional which is great IMO. Everyone wins in that case, you can get Windows to work like you prefer in a supported manner. Sounds positive.
Now, if they officially sanctioned running Metro apps in a Window (on a desktop or laptop) I would be giddy. I like everyone wins scenarios.
Stardock have shown MS how to do it - Start8, ModernMix and DeskScapes - the functionality of these 3 add-ons would satisfy a large proportion of the noisy objections to Win8, and significantly reduce the 're-training cost' argument that keeps coming up from business users.