And actually that's exactly what the FreeBSD Jails paper says too. Their aim was to make uid 0 more granular by segmenting the system so that you have different access control in those jails.

You see some of these ideas in Linux, but as with all Linux kernel technologies they all feel like they've not been written with a design in mind from the start (just look at epoll, namespaces, /proc, and so on).

All UNIX flavours are pretty late to the party though, even plan 9. This sort of isolation was a feature of most capability operating systems since the 60s.