I'm hoping it isn't time travel.

Actually, I'm hoping the meat of this game takes place in the Warriors of Darkness' version of Eorzea... which apparently a bizarro version of our Eorzea.
Which is why Urianger is a healer and Y'shtola(Matoya) is a DPS, and they were black instead of white... and Thancred is a tank and he wears white instead of black...

Then this raid would take place on the "dark" world (Which I desperately want to call the "World of Darkness" but that's already taken...) as perhaps a revival of some ancient tech... Allagan or otherwise.

This would be why the 2B featured in the promo image is the "bizarro" version with dark hair and white clothes and perhaps why it is the "Dark" Apocalypse.