There's little to write about here except it is so. Since I do map from 8.x to 10 and back something's not right about those that told you no. But the root? That's been a security risk for so long and good to see it's been welded closed. If I did need to do something to the root area, you use other methods.
Had 2 Windows 8.1 computers on peer to peer. Shared c drive on one and on the other mapped it as H drive. Second computer crashed and had to install Windows 10. Now I can map a folder from the first computer but when I try to map the c drive as H: it says I don't have permissions. Does Windows 10 prohibit you from mapping the root drive of a computer as a drive letter on the Windows 10 Machine. Microsoft Support was absolutely no help. They said you cannot map a Windows 8.1 system to a Windows 10 system. I'm still laughing.