We actually had an IRC channel for TMX. The link to it was stickied in General Chat forum on United TMX for a long time. Hardly anyone supported it. And when I say supported.. I mean no one idled there.
I think it's probably due to the fact the majority of players/builders here aren't savvy enough about old technologies like IRC to make use of it, and also due to the fact they don't understand the concept of idling. They join and see 15 people in the channel and think they must all be active. They say "hi". No one responds immediately, so they leave.
I'm not against IRC. I idle (and occasionally chat) in #maniaplanet on QuakeNet, a bunch of channels for my Minecraft servers, my old clan's channel on EFnet, and in some developer's channels on EsperNet. I also used to hang out on #et.tm on Quakenet. A lot of well known TM players hang out there; mostly those that are around the eSport scene.
I've had almost a 24/7 presence on IRC since late 1998. So I'm certainly not against the idea. But we just haven't had good success with a TMX channel in the past. I don't really see that changing. It's an old technology for, mostly, older users.
The forums here are really the best way to meet up with people and communicate across timezones. If you need to do something more one-on-one... I'd opt for Skype or MSN or another IM service these days. Some of these even have a group chat function if you need to organize something with multiple parties. It's how I usually organize duo tracks and the like. And if you're doing such a project, it's probably going to be with someone you already know anyway.
Finally, adding a chatroom on the site itself would be really hard to moderate, and we'd need people to watch it 24/7 otherwise it could be overrun with spam. I'd say it'd be more prone to that than even the chat in-game on a server.
In my opinion the forums, augmented with existing IM services, is sufficient for our needs on MX. Maybe MrA and Forzyy would have different ideas on it. But those are my personal views.