These efforts are in their early stages. A developer called "Lemon1Ice" told Windows Latest that Windows 10 on Arm can be installed on the OnePlus 6 and is being ported to Xiaomi's Mi Mix 2S, but much of the operating system (OS) is unusable. Another developer called "Enviso0n" is attempting to bring the OS to Samsung's Galaxy S8.
Windows 10 on Arm enables this kind of tinkering because smartphones and so-called always connected PCs use many of the same chips (often from Qualcomm). Microsoft didn't intend for the desktop version of Windows 10 to reach smartphones, but the shared Arm architecture makes it possible, at least in theory.
Like other projects, these efforts might serve little practical purpose. Microsoft announced in January that it would end support for Windows 10 Mobile at the end of the year, indicating that people don't even want to use a mobile-optimized version of Windows on their smartphones. Who'd want to use the full desktop version?
The real value in these projects comes from demonstrating the power of the Arm architecture and the value in supporting it. Microsoft brought Windows 10 to Arm, so it could make PCs with Qualcomm chips that never have to go without Internet access, and in doing so, it opened up a world of possibility for many other devices.