Seems like that would take up a lot of bandwidth, and it would probably end up showing people frequently due to background noise, keyboard mashing, etc. I think I'd find it too distracting, personally. I had to revert to an older version of skype because they kept adding things like this (I don't need a giant version of somebody's avatar flashing up on the screen every time they make noise!).
webcams are a bit too much of an invasion of privacy. we don't want to turn quake into chat roulette...
user-selected avatars might work though. there won't be much difference when its only 64*64 anyway.
you could add location information and spacialise accordingly (but may be considered a cheat), and make sure names are highlighted etc though.
personally I've been working on xmpp support, that is:
a) chat via xmpp (read: googletalk).
b) exchange IP information using Jingle+ICE in order to establish (coop?) games directly without needing to mess with firewall etc rules (or voip without server extensions).
using googletalk and oauth2 allows you to connect without telling the engine/plugin your google password (you tell your password to a browser and get some auth token to paste into quake - which is a user-interface nightmare, but does otherwise work).