I am really curious about how much parsing and formatting occupy *nix source code. (IIRC 30% of ls), and if it would be a good idea to decouple the way you mention it. my json-infused distro is still on my mind.
ps: this lisp machine talk mention how 'programs' (I guess functions) exchanged plain old data rather than serialized ascii streams making things very fast. There are caveats of adress space sharing though but it's another nice hint we could investigate other ways.