If you could write an OS from scratch...

Okay, so most every OS out there is C-based.  If you could magically write a complete hardware-controlling OS all the way up to the UI and applications using a different language, which would you choose?

Though I like Lisp, I think I'd have to choose Erlang, maybe NewSqueak for embedded/smaller systems.

Please go search for other OSes and how they are implemented. LISP OS, done.
OCaml OS, done.
F# OS, done.
Haskell OS, probably done a few time.

The issue is the lack of adoption and lack of apps. So shut the fuck up, get your OS done and then make compatibility layers to let the unclean in.