The only mystery I can think of here at 3 am doom scrolling in bed is meracidia.... But we know a decent chunk about the place already as it was referenced over the years.

We know bahamut was a result of meracidia. They had a war with the allagans. The warring triad originated from there. Emet selch wanted us to go there so we will probably after DT.

So unless the writers pull something out of their ass, we know that they will probably not like us when we get there, there's gonna be a big bad thing for us to fight as a lvl 93 trial boss, lots of allagan resentment, probably get to meet dragons that know tiamat and stuff like that and learn about dragons we already know.