When Windows RT launched in conjunction with Windows 8 in 2012, the operating system ran on ARM-based devices with desktop program support only for software that Microsoft bundled, like a version of Microsoft Office. Because of RT’s inability to user-install Win32 programs, and for a number of other reasons, the operating system failed to catch on. Microsoft's last RT device, the Surface 2, launched in 2013.
Now, new documentation appears to show that Microsoft is working on a “full” version of Windows 10 with Win32 support capable of running on ARM chips. In addition, there’s mention of a Windows 10 version running on x86 mobile devices. First discovered by Twitter user WalkingCat, the documentation is found on a MSDN page describing an Audio Engine Core Test.
Targeting non-phone devices, the first bullet describes “Windows 10 for desktop editions (Home, Pro, Enterprise, and Education) ARM”. While people in the mod community have changed Windows RT to support the installation of Win32 programs in the past, it appears that Microsoft itself is working toward further compatibility for ARM.
The last item is “Windows 10 Mobile x86” which could end up being powered by an unknown Intel processor. The persistent rumors a Surface Phone have been stoked recently, in light of Microsoft CMO Chris Capossela hinting at the development of a such a device. However, it's possible that any emulation work in the ARM version of a full Windows 10, listed above, could be modified to work inside Windows 10 Mobile for ARM.
A Surface Phone running a version of Windows 10 Mobile supporting Win32 desktop-style applications would vastly increase the application support for Microsoft’s phone platform. Such a device may not have much utility in a mobile form factor for most consumers. However, Continuum’s power to project itself to a monitor and support peripherals like a keyboard and mouse would make such a device a true mobile desktop.