Those clouds rolling in is
the same visual animation used when the Starshower appeared over Eorzea in 1562 after the Battle of Silvertear Skies. The clouds roll in, then burst open into the Starshower. Which implies that it's perhaps being seen OUT-OF-ECHO for the first time in 15 years. And on the First to boot...
In 1.0 it was almost certainly tied into the derailed Presence of Silvertear Lake storyline, but the Final Days is a great opportunity to tie it all together in a clean way that will easily pass for totally-planned-all-along. Ever since the story changed trajectory, the Starshower has awkwardly just been "that thing that appeared in the sky when the Echo sounded and then now people see it in a vision when they're chosen for the Echo". Leaving it at that was fine, but admittedly awkward and anticlimactic. Attaching it to the Final Days tidies things up a bit. Can you see the stitches? Yes. Is it better? Also yes.
This lore / writing team is
too good, lol. I half expect them to go back and use the Presence of Silvertear Lake when all of this is over just to bring it all full circle with no loose ends and do a victory dance on the apex of this story for all the trouble it's given them.