Marking this as a feature request, but personally, I don't see it happening.
There is a reverse-engineered solution for Pidgin (and other purple-based IMs), see http://code.google.com/p/pidgin-opensteamworks/. I haven't actually tried it, keep in mind that it's not supported and might be against Steam ToS / other policies.
Nothing extracted yet.
The protocol should be opened to allow integration into telepathy-based clients (the messaging service Ubuntu currently uses).