The question is what new function Plan 9, as an OS, defines for
the end user.
Plan 9 is not for end users.  Plan 9 is for programmers.

I think I just heard the sound of a nail being struck on the head.
 
I do find myself wanting Lisp, Scheme, and Haskell and all my other weird programming toys for Plan 9 too.  I believe Haskell and Scheme are handled, but has there ever been a Common Lisp implementation for it?   Perhaps I should look into a port of SBCL or something.

Dave

-rob