wrt #4: No, the big thing about Plan 9 is that each process has its own view of the filesystem, and can modify it without any privileges. This would break the unix security model because unix has setuid.
> Imagine that Unix had this feature and still had setuid, and you would like root privileges. No problem; make a custom namespace for /etc that has a version of /etc/shadow, /etc/group, and /etc/sudoers that have known passwords and list you as authorized. Now run sudo. Done.