The lack of something like this is one of my few major disappointments with this game. We had some great conversations on the general chat back in Aion; they kept spam out by making you wait 30 seconds between posts (Which was a bit long, but 20 seconds would probably be reasonable!).
There were separate global LFG and Trade channels, so while you could get away with posting group invites or ads VERY occasionally, if you were obnoxious you got shouted out of the channel and blocked by most of the server pretty quick, so spam was rarely a problem.