Only way I see a world chat ever working is if they put a timer on it so you can only send a message once every 3 or 5 minutes. That being said, the central city may be Ul'Dah now, and you may not like it... But once ishgard comes out it will be the center for trade and grouping. All the other three cities will likely be reserved only for new players, and people doing class quests for new jobs they're leveling. They'll be ghost towns, kind of like bastok, sandy, and windurst were in jeuno, and then White gate days.