I'm not sure about this.
Server-wide invites would be very much welcome in an environment where you have a server-wide channel of communication, at least in cities. Kinda like WoW's "General" channel. But while it's very useful, it's not very "FFXI-esque", also developers already stated that with the current FFXI infrastructure such a possibility would be a very heavvy burden for the servers.
In light of this, I think server-wide invites wouldn't really be useful.
The fact they updated /PCMD to work region-wide some patches ago is good enough, imho.

What they should do is make /shouts zone-wide. Currently they have a certain range (100 yalms radius? 150 yalms?) from the person shouting. In some particularly large zones you can't possibly reach everyone. Say you're in Valkurm Dunes asking for help, or for a Raise. You're shouting but the only person willing to reply to your shout is too far away, so they won't read it.
I think shout should really be made zone wide, possibly increasing the amount of seconds between each shout you can make, to avoid the same people shouting too often.