It's been discussed so many times before, yet we still don't have an answer. Part of me thinks we'll never get an answer, and that it was simply a concept that was eventually abandoned after they started work on the trailer. Either way, the lack of an answer has slowly been eating away at me, so here's yet another thread in hopes of finally getting some light shone on this by a rep.

I'm talking of course about the Adventurer's Guild.
http://i.imgur.com/EIwjX.png

As it stands, we really only know of three city-states that we don't currently have access to. Ishgard, Sharlayan, and Ala Mhigo.

Ishgard seems unlikely, as it doesn't appear to have any domed roofs: http://i.imgur.com/SxbXG.png

Unless the center of the castle is hollow: http://i.imgur.com/GqxKM.jpg
Even then, it's a stretch since the sky above the dome seems to be free of any surrounding structures. Plus, in this shot you can see outside the guild and the sun appears to be shining. There also seems to be towers in the distance: http://i.imgur.com/WiZ3S.png

We know Ala Mhigo was conquered 15 years prior to the start of the game, and I think it's safe to assume that Mor Dhona was destroyed around the same time, since it was supposedly Garlemald's first incursion into Eorzea - the two events would have occured around the same time. So if the character is in fact experiencing the echo, that would mean Ala Mhigo would have already been conquered at the time of the trailer, which pretty much, though not entirely, counts it out as a possibility.

The only thing we know about Sharlayan is that it is in ruins because of the Garleans. Again, most likely around the same time as the fall of Ala Mhigo. Plus Sharlayan appears to be far up north, and the flora within the guild doesn't really seem like it would grow that far north.

Is this just a concept created for the sake of the trailer, or will we actually see this guild and it's corresponding city in-game at some point?