It’s a thing born in google. It shows. The reasoning behind problems and solutions is so abstract that makes for a beautiful paper or a nightmarish reality. In the ‘80s there was a little known machine, called the Commodore Amiga. Paths were addressed by a volume:folder/file schema. Apps had logical volumes too (progdir:) and the os injected others (env: temp: fonts: ..) guess what? Just use that schema and control what an app can access or not. If you don’t give me a volume for a disk, I cannot make my way to it if it’s not collated into a mountpoint thing
For those uninitiated to Plan9, binds are basically the replacement for symlinks (they're kind of like a mix of mount namespaces and bind mounts but more fundamentally baked into Plan9).
