You have to use the ocarina of time to switch between worlds,
Heres my guess. This has to take place before the great war, probably soon after Jeuno was established, i think a bunch of us are hoping to participate in the war, but i dont think SE wants to do rendering of damage to places as it happens.
It can't go back to the kuluu or zilart times because jueno wasnt established then. SO if im right about the time frame, then there will be some sort of villain who is probably angered at the course of history, who goes back in time to stop the shadow lord from being killed the first time. I'm hoping for alot of Raogrimm, Zeid, northlands expedition cameos, and you helping to keep them on the right path.
I'm also hoping we will finally find out where the ferry in norg goes to, they wouldn't render it if it didn't eventually have a purpose (much like how the trees near the swirling vortex in Valkurm magically moved over when COP was released)
I'm finding it fun to guess, there are alot of clues but you never know how many of them will lead nowhere, maybe the city of Tavnazia will be available.
something about the final CS in the AN fight made me think also, but i don't want to cross into spoiler territory.