A full NT-based Windows 8 running on ARM devices would be amazing. The end of the Wintel monopoly? MS has kept its Windows NT 5.x/6.x-based products (Windows 2000, XP, Vista, 7, and server editions) Intel/AMD-only for over a decade now. Let's hope Apple follow suit, ditch their crappy iOS for the iPad and release a full ARM-based Mac OS X-based tablet (perhaps with an iOS VM for backwards compatibility). Then Linux and BSD (and ARM AROS?) would have some healthy competition, and the open-source alternative could improve too.
IMO, Microsoft would be foolish not to implement some sort of JIT-compiler for running x86-compiled Windows apps on ARM Windows 8. (Much like Apple did with Rosetta for running PPC-compiled apps on x86 Macs.) Sure, it would be considerably slower than native ARM builds, but could serve as a decent 'stop-gap' until all popular Windows apps get an ARM build. As well as a means to run some legacy Windows applications and games.