(Hmm, sent a reply by email, but it's not showing up here???)
I'm working on such a thing, but there are some things to consider:
This is not an easy thing to make, and it will have a fair bit of impact on the vBulletin system. That is something I want to minimize at all cost. I think it's possible to do this without changes to the database, so at least we have that
Other things to consider: the time out. People in chat are no longer active under "vB terms" (as they are no longer browsing the forum, or whatever), which means their session will time out within 15 minutes or so. Any hack to display users in chat will have to deal with this stuff, which makes it much harder, especially since I want to minimize "hacking" at all costs.
Something else to consider: any such code might become totally useless with vB3, so is it worth the time or effort right now to create a hack that will surely NOT work under vB3?!
That doesn't mean I'm not looking into it though, hehe
Oh, those who peeked at our forums and noticed the one lined "users in chat" up and running there, the code for that can not and will not be made public
Oh, and version 1.4 of this hack is about ready, very much the same, but without that checking array, so setting particular sizes should be easier.