The first Xbox-branded handheld console is here, but it’s not made solely by Microsoft. Instead, it's a partnership between Asus and Microsoft for a new version of the latter's ROG Ally handheld consoles,

As in SteamOS, a traditional desktop UI will reportedly still be available on the ROG Xbox Ally, but you have to specifically decide to launch it. Hopefully, any version of this interface that also rolls out to generic Windows PCs would also be able to save system resources by shutting the traditional Windows UI off entirely.