You sacrifice official support and updates, which coming from Microsoft, could mean a lot of things.
Yeah, it's there.
I believe if you kill the 11 taskbar, you'll find 10's underneath. I found a video of it somewhere.
I'll give you that one.
Local vs. Internet accounts is kind of different though. You need to make a Microsoft account if you don't have 11 Pro, a small inconvenience, but annoying. There are a lot of people who need those weird business specific features and they can't sacrifice $100 for a file that is easily yo-ho-ho'ed.
And yes, I have used 11. It... is very sub-par.
Microsoft needs to work on

legitimate features and upgrades

with another OS.