Re: a ha ha ha ha ha :(
"Windows already supports Arm, IA-32 and x64 which are by far the largest current market segments. And Windows has previously supported Alpha, MIPS, Itanium and PowerPC, so additional processor support is not a problem if there was a need for it..."
That's a rather rosy viewpoint to take of Windows cross-architecture support. Windows supports x86 and x86_64, yes. Support for anything else has to be qualified, and a lot of it was never very useful.
Windows has had some kind of ARM support for years. It's biggest success in this area was Windows CE/Windows Pocket PC. Of course Windows CE and company wasn't really the same operating system as Windows on the desktop. It had its own set of software and not much in common other than a standard approach to the UI. It fell into obscurity with the rise of the touch UI and the operating systems that relied on that scheme for mobile devices.
Now Windows supports ARM in a different way. It's approach this time is similar to that of Android to run common software on multiple architectures with a virtual machine or something like one. Of course that approach has its limits, but it has its advantages as well. The problem for Windows here is that there is not a lot of software that runs that way. Most of the applications for Windows, especially the popular ones, only run on X86 variants. Windows has ARM support, but not for the programs people think of when they think of Windows.
Windows used to have Apha, MIPS, and PowerPC support back in the late nineties. However, not that many apps were ever released for those architectures (and almost all of the few that did were server applications), and Microsoft ended support. Again, the Windows applications for x86 wouldn't run on those systems. A similar situation existed for Itanium later on.
So yes, Windows has nominally supported a number of architectures at different times, but none of them have had the applications available to make Windows a real success. At this point Windows has basically been stuck with x86 based architectures. Theoretically, if x86 based architectures were to be cancelled, then application vendors would port their applications to whatever Windows moved to. However, that is not likely to happen.
Of course open source software tends to adjust to different architectures more easily. Most Linux applications have been compiled for a number of architectures because they are open source. This makes is so Linux has been ready for ARM, MIPS, Power, or Itanium, etc. desktops and servers for a while.
However, this doesn't make Linux (as in GNU/Linux, the operating system) ideal for mobile devices. Right now, Android and iOS are the successes there. Will convergence ever actually happen (with Windows RT/Modern UI, Ubuntu Snappy, Android, or whatever)? I'm not sure. There are many issues to be dealt with. It seems to me that you would need to have either two sets of applications that ran on the same base, one for mobile interfaces and one for desktop interfaces, or you would need to have one set of applications that had dual interface modes.