My experience with FFXI amounts to trying out the free trial about a week ago (and it didn't run that well to boot), but I've always had an interest in multiple worlds and such. If we're given more lore on this, I can see myself trying to figure out ways to weave it subtly into my character(s)' backstories. It wouldn't be anything too blatant, but it might help give explanation to a few events, and perhaps future backstory for possible alts. The Vana'diel aspect does open up a lot of potential for ex-FFXI players, as I've seen quite a few that recreated their old characters in the new game.
