1) It would be extremely helpful ( for obvious reasons ) to have a chat channel that ran through all the major cities. Perhaps this would even encourage people from leaving Ul'dah once in a while...
2) A trade/crafting/repairs channel would also be nice and useful
3) A looking for group/leve link/linkshell channel would also be very good. You know, somewhere to socialize and get together with people outside our LS network.
4) Perhaps also a global channel that can be seen throughout all the zones
The lack of some kind of far reaching channel, whether it even just be connecting all cities, makes it even harder for us as a community to come together and do stuff. There are so many barriers to overcome as a player trying to enjoy his or her time in Eorzea, why add more barriers by making communication so limited and difficult? A HUGELY important factor in MMOs is the ability to socialize and connect with other players. Developers have not done nearly enough in this regard and this, imo, should be a top priority. And while you are at it, add a good quality party/group search feature. Social aspects of this game have been so neglected while you Devs try to sort out the technical mess you are in, but the social improvements suggested here will help the player base create their own fun while you guys sort out your own problems.
If your concerns are that these features can be exploited for gilsellers etc - lets just be realistic - I can assure you that such a problem would be a honor and luxury for you to have. The population is rather small and I doubt any goldsellers will be trying to turn a profit in this game at the current time. Perhaps that is a problem you should worry about when the time arises and not let it interfere with things that could otherwise make this a more enjoyable game right now.
Thanks for your time.