Microsoft had the opportunity with Windows RT to extend the Windows ecosystem to ARM. However they decided to:
1) Artificially lock-out desktop app execution unless properly signed
2) discontinue Windows for ARM (at least from product perspective, internally they certainly still are compiling Windows for ARM)
In particular 1) was a stupid move, as you just had to recompile Win32 Apps to run under Windows RT. CLR/.Net apps were even running as is. Microsoft had a full featured Windows for ARM but stumbled over their own stupid decisions. Would not surprise me if 10 years down most would be running desktop apps under ARM, but it would not be Windows because Microsoft missed the boat and locked itself into x86 territory.