You shouldn't bring up Plan9 when discussing Linux.

It's akin to bringing up Mozart's writing symphonies at the age of 8 to the proud mother of a somewhat disabled child that has finally mastered the potty at the tender age of 12.

Seriously, you can literally list every single new IPC introduced in *nix in the last 3 decades and counter it with a better design and execution under Plan9. It's simply the result of a proper design as opposed to an afterthought. No real point in bringing it up unless you can constructively use the information to fix Linux.