MS will provide OEMs the software they need to make whatever devices they'd like. However, they will not be making another piece of mobile hardware. If the market indicates that people would like a more portable Windows device with cellular bands then I am sure someone will release it...however, I doubt that will ever happen again.
All MS really had to do, from the beginning, is support their own devices. They didn't NEED third parties to make the platform successful...just like Nintendo hasn't really needed third party developers to support their hardware - they support it themselves.
MS had the technology, franchises, and OS to make this a successful platform and they, literally, did everything they could to destroy it. They convoluted and fractured their own market so much that it actually became more difficult for them to release decent apps on their own devices than it was for them to release them on iOS and Android.
Exactly every time their mobile offerings picked up steam they pissed off their fanbase, reset, and moved to something less interesting and functional with even less support.
This "we don't need a 3rd ecosystem" stuff is trash. I can't think of any product in this world that doesn't need more than 2 offerings. Just because they destroyed it doesn't mean it was impossible from the beginning.
Regarding the concept. Yeah, it's interesting but might as well be held by an alien. It's completely impossible for anything like this to be released for decades.