I'd say we have a system for that purpose already? Its not a chat, though - its the partyfinder, where you can set up a party for any duty you want and look for people who'd like to join you. Its even visible to the whole datacenter, not only to the people who are in the chat and are actually reading the chat at the time of your request - so to me that sounds like an even better option than a chat where your message might get missed.
I understand that a lot of people miss the community aspect of the novice netwok and just having people to talk to, but I'm still unsure if some kind of "global chat" would actually solve that problem. Personally I believe that a "partyfinder" or "marketboard" for FCs and linkshells, where people can advertise their FCs/LS if they want to and anyone looking to join one, can freely browse and find something that fits their intrest, would be a much better solution than just a random chanel. Could help with finding an FC that is actually what you want it to be - helpful - aswell...
But just for the purpose of finding a party to clear a certain dungeon with, partyfinder (or even dutyfinder) should do the trick.
As a last note: Anyone who finds themself waiting in queue (or in PF) for a rather long period of time (30min+) should evaluate the following things:
1) Are all your languages ticked?
2) Does your timezone match the servers timezone? By this I mean: Does the time you play match the peak-hours of most people on the server? If it turns out that most people are asleep or at work while you've got time to play, you might want to consider moving servers - for example: I live in germany and I play on a european servers, so my time matches the servertime (more or less). A friend of mine who also plays on the same server is from the US - when its about 6pm for her, its like 1am for me and give or taken an hour that time for the whole of europe, so if her queues are a bit longer, theres no surprise and moving servers would probably fix that.
3) Consider playing a tank or a healer - I know not everyone likes that and everyone should be free to play what they want, but... might be worth evaluating whats more important to you: Fast queues or playing a dps.