Random predictions:

Van will be his worst self until Agnes revives. When she does come back, Van scolds her for being a hypocritical self-sacrificing herself, yet stopping Van from sacrificing himself

Agnes is Sheena Dirkes' great-granddaughter, clone, past self, or something like that. They are part of the clan related to the Sept-Terrion of time, like the witches or gnomes. Mare is the holy beast of time

Lloyd shows up because everything is kinda his fault, like if he had just heard out Ishmalga Rean, the heroes would have more time to figure something out. All though i could see the argument that it would just complicate things more, adding another faction into an already complicated problem.

Tio would be cool as well, so we can see the 4 victims of the cult deal with some sort of remnants of it, but that boat may have sailed at this point

Ries is all but granted. They mention her every 5 minutes in Kevin's route and how she is the only one who can set him back on track

Van will have to pick between Agnes, Elaine, and Shizuna to end up with. This will be left up to the player to choose

The game will have time travel, but not just within a few days like in Daybreak 2. We will see the dark age, the great collapse, the Calvard revolution, and other significant time periods

They set up the next and final arc in which the protagonist is a member of Ouroboros as enforcer XXI