Well, leaving random messages isn't something you could stop, anyways. But when you have a place for real time chatting, it's the best place to do real time Q&A, of course. So a chatroom of sorts would come with both and hopefully would have both and not just one of them.
Right now the argument against having something like that is that it would direct people away from the site, in a way. Of course it would only be completely off the site if it's an IRC channel and not a chatroom that's a part of this website, but it would direct conversation away from these boards. In my first reply, I did mention about the whole wanting to have some more permanent chat and answers on the forums first, before it is directed somewhere else. If we did it right away, we'd lose tons of good stuff that wouldn't be easily accessible to our users. And we really do want to have a lot that is easily accessible to our users.
For random messages right now, off topic's chat thread probably works well enough.