(Big spoiler) Future content could be based on...
This is actually a repost of a post I did earlier this morning on reddit. Beside the speculations, I think it explains well how FFXIV connects with another chapter in the series.
First of all, if you haven't finished the main storyline, close this post now. I'm going to spoil the very end of the story. don't spoil that to yourself, it's really fun, and it will give you chills. Just take your time and finish it, it's not worth ruining it by reading a post on reddit. To everyone else, what I'm going to talk is so huge that it could be the theme of a whole expansion, if not more. I'm not going to talk about the upcoming content like crystal tower or the next turns in coil.
Well this is coincidental as well
Anyone who has followed the FF series, knows that FFXII was based off of FF:T. Ivalice, the localities, etc.
One interesting thing is the level of advancement of Airships in FFXII was very similar to the level in FFXIV. The Airships even look to be of a similar design. The "Empire" in FFXII also had Judges who look remarkably similar to the hierarchy in of baddies in FFXIV. Those two things were very apparent to me, but Gunblades and the aforementioned Third Eyes were not in either FFXII or FF:T.
The other thing I've noticed is the map of Eorzea and the map of Ivalice. Here's the map of Ivalice:
http://oi42.tinypic.com/2vbkdog.jpg
Take notice of the bottom continent of "Lionel"... That is Eorzea...