Yeah, I noticed that comet too, I'm wondering if that comet triggers certain events in Vana'diel's history to come forward and become part of the present (linking to the phrase off the German site "Geschichte wird zur Gegenwart" - "History (as in the "The Past") becomes present") and the players have to move through certain events to act through the events of history (linking to "A Tale Once Lost... is about to be retold", it recalls what happened to this lost part of History and tells it to players) and it could occur something sinister like changing history through the events of the antagonist, the player will have to prevent history from changing for the worst for Vana'diel and her people, even if it does mean the orcs taking over Davoi.
Maybe all the events that the player manages to keep safe will eventually lead up to the battle of Tavnazia (Maybe we will actually ENTER the City waaaaay before the events of the battle) and fight the battle to protect the city until the "orcish weapon" destroys the path to Tavnazia making the peninsula an island. Eventually, we would fight the antagonist (as usual, and after find out some of his/her/it's backstory and why they're doing it) and fight him to stop any further damage to history, but still have access to each part of the history of Vana'diel without actually damaging the timeline.
I'm very interested in how SE will make this expansion and what activities will be in store for us adventurers, maybe some more mid lvl and end game camp sites, some more equip accordingly for mid lvls-end game, more crafts, more job improvements (please more PLD stuff! lol) etc. Winter doesn't seem to far away now lol.