I've been able to (and have done so) plug my android phone into a usb hub with mouse and keyboard and into a 1080p screen for quite a few years now.

Of course, there's relatively little that truly takes advantage of that set up, and making the user experience more pleasant would make a huge difference, but android understands mouse and keyboard input just fine. Microsoft may be somewhat further along on this front, but I don't think it's as much as you think - the apps that can run in this way are not full windows applications, and there are relatively few of them at present.