Windows NT was born on the MIPS platform. MS has also had NT on PowerPC, Alpha, and SPARC... not just the kernel, the whole OS.

Two problems. Onw was simple: Microsoft used this very existance to bleed money from these various chip makers. They didn't just support Alpha, they had DEC doing the work AND paying for that. Same with Motorola.. Windows 2000 didn't show up on PowerPC because not only did Motorola have to do the bulk of the programming, MS wanted $20 million or so for that ability.

Second... no promotion. The on real power Microsoft has with Windows is the ability to move platforms... but that only happens when they push it. So, no alternate processor mandate meant very few apps on non x86 versions of Windows. Kind of like 64-bit on XP. Once Microsoft required drivers and apps run on 64-bit Windows to get certification, 64-bit Windows became a reasonable OS.

MS will have to make Windows on ARM their OS, not try to stick ARM or Qualcomm or nVidia with the bill. And they have to require ARM support as part of driver and app certification, or the port will be pointless.

And even then, there's the bloat factor. One reasson ARm tablets are revitalizing the tablet concept is low power. And sure, price. But also, they're all running reasoanable operating systems, and they're at the top of their class in performance... iPad and Android tablets are the fastest iOS or Android devices, in general. How do you scale dual core Imtel desktops down to ARM tablets, Windows or not, without making them just as terrible as x86 tablets running Windows?