This feels like deja vu. Wasn't there recent Win 8 related info that indicated that it would have an "immersive tablet UI" present? And this UI might ship even before the full version of Windows 8? This is possible since it is essentially a SilverLight+XNA "sandbox" environment which hosts completely managed applications that are portable between multiple hardware devices and architectures (x86, ARM,...)
I find it interesting that this follows almost exactly the suggestion I made a long time ago about such a portable UI that is equally at home on a desktop, a tablet or a phone, and can either be an additional UI (on desktops and some more powerful tablets), or the one and only UI (on lower-powered devices).
So to me this seems pretty clear what MS's plans are regarding this topic.