Sounds good, but grandma will need to disable SIP, run a few commands using sudo, and add a root account from the recovery system. It's Unix in the same way Windows 2000 was POSIX compliant, you just need to reconfigure the default system.

The Linux desktop is widely used all across the world in the form of ChromeOS and, if you count touch screen devices, Android.

Windows 2000/NT POSIX support was the bare minimum, it isn't comparable.

It only got usable when SUA came to be.