"It doesn't look like Microsoft is going to allow you to select you own User name, and possibly even the ability to change to a local account will be gone"
My apologies if I speak in ignorance. I have not been following this thread, as far as the thread title was concerned, but I was drawn to your comment , Saltgrass.
I still have my username , let us say, in windows explorer - users. That is "David"
When Windows 10 tech preview was first put out, I was annoyed to find that it changed my username to the first portion of my MS account - davehc, all small letters. It glared out looking very dumb in Windows explorer.
But the answer was easy. Since then, I log in with a local account, giving myself the username David. As soon as the remaining formalities are complete, and I arrive at the desktop, I go to the settings accounts and logo in, and "switch" to my MS account. This combines the two and keeps my original username as the only user.