I wonder if the catastrophe will have something to do with Atherytes, especially after seeing the blackened out notes on some of the concept art and that "unusable Atheryte" CG which looks like those "things" piercing the earth on other concept art. Maybe the Garleans will overload the atheryte veins and they blow Eorzea to pieces, and since there are big Atherytes in all major cities....
Or there'll be disaster much worse and terrible than we can imagine. But i think it'll be connected to the aether too.