If you found this interesting, you may also like GCLI (as featured in the Firefox dev tools command line - or you can play with it here: http://mozilla.github.io/gcli/ ).
That said, that's a great topic to cover! I think GCLI does a pretty good job of command completion. The Lisp Machine did as well. I have friends who love some of the router CLIs, but not sure which one(s).