[justincormack]

The ideas from Plan 9 are very compelling, and parts of them, like namespacing, have been adopted, thats why we have Docker now to some extent. But for operating systems, build from scratch is hard, there is a lot of code. But it is getting easier. See it as the prototype...

[stormbrew]

Plan9-style namespacing -- as something that users can do directly without privilege -- has definitely not been adopted outside plan9. What we have is a pale pale shadow of the capabilities exposed by that.

Unfortunately, true user control over the namespace is incompatible with the unix security model (thanks to setuid being the only means of privilege escalation), and the namespace compositing that makes, for example, just stacking bin directories onto /bin instead of using a PATH requires that it be possible to have more than one file with the same name in the same view to work well, which is (probably?) incompatible with POSIX.