Who knows? MS might be obsessed enough with backwards compatibility to pack an emulator in there, like they did with WOW64 (though it would be more difficult to write an x86 emulator for ARM).
Building an x86 emulator is easy. Building one that can run Windows 8 software at speeds comparable to then current Intel or AMD x86 processors will probably be impossible. There is no such performance gap between ARM and x86.
I can see ARM being great for corporate desktops: .net LOB apps work, IE will work, Office will work etc.
The performance of a built-for-speed x86 is very forgiving. Eclipse runs well enough on my Core i5, but I suspect it would have problems on an energy-efficient ARM.