Two things I, as a newcomer, just noticed

[Anonymoose]

As for the aetherytes, it's as Belhi said. As Dalamud drew close, the aetherial networks (the rivers of aether that flow under the ground) were thrown out of wack. Some of it was the doing of Nael van Darnus, who had been measuring and screwing with the network from the start to feed aether to the moon. After it got close enough, Dalamud itself was drawing aether to itself. You can see it rising during the scenes with the deaths of Garuda and Nael van Darnus himself (actually Eula Darnus herself).

The aetherytes in the game actually changed while the game was live - they became overaspected, warping the fabric of the corporeal world around those locations. Atomos would come through and start sucking aether out of the network through the aetheryte like it was a straw, tearing open rifts that caused voidsent to flood though. Teleporting at the wrong time would see you instantly destroyed by a mass of skeletons, ghosts, ogres, and the like.

The Calamity destroyed a ton of aetherytes, but many that were left were garbage. Some were destroyed by meteors, some were "radiotactive" (corrupted crystal), some warped, etc. If you go west from Mor Dhona, you can see the ruins of the 1.0 camp and see just what became of that particular aetheryte. You can see another in the western Highlands.

The Sharlayans repaired the network themselves, with Ul'dah footing most of the bill. This is why you have to pay to teleport - to repay this massive debt. You'll notice other aetheryte types around the realm, though - those have other origins.

As for Midgardsormr
This line was deliberately worded to confuse and cause speculation. It's the only such hint of its kind, making it more of a PLEASE LOOK FORWARD TO IT than anything. One day, the truth will be revealed. Is he from the original version of The Source? Is he from a godly realm? Is he from that dragon star that the Ishgardians like watchin' so much?