1) They won't reveal everything at 1 live letter, they will tease us until we are like a month away ( or perhaps at E3 2015, drop the bomb then).

2) I suspect there will be some sort of content revolved around the 4 houses of Ishgard ( maybe something like Conquest in FFXI or something else)
3) They didn't go into full detail on what the FC airship content will have, so for all we know, there could be quite of few big reveals there.