Have you thought about integrating/leveraging Ace (previously SkyWriter, Bespin)? http://ace.ajax.org/
This would give you the ability to let people use emacs/vim shortcuts among a lot of other not-reinventing-the-wheel kind of things (like better syntax highlighting).
I have, and originally intended to. However, I went with something a bit simpler to implement to start with, as I haven't played with ACE in any significant way and I built this over the weekend.
It's definitely something I would consider to support.
This would give you the ability to let people use emacs/vim shortcuts among a lot of other not-reinventing-the-wheel kind of things (like better syntax highlighting).