Sure, but there's still an established concept of "ship an ARM tablet and get people to develop for it". In other words, there's no Wintel monopoly to contend with as there was before. I think that's largely what NT-on-not-Intel fell victim to, despite coming from one of the Wintel companies.
I wouldn't be surprised at all if they come out with windows phone 8 based on windows 8 and not windows mobile. That way they could have one os for phones/tablets/pc's/ect. They could use their market/repository as a way to force people to modify uis. Since all of the 3rd party apps are written in a version of silverlight(they haven't dropped this restriction yet right?) it should have few incompatibilities.
Unless Microsoft wants to ship an installer that jailbreaks and installs W8 on iPads.