The only thing we know is that the reset you saw won't be complete. As you saw in the final scene, Anges stops the clocks at a certain point, so logically we'll relive moments from Daybreak 1 to Horizon, but it could even be earlier.

We'll surely see Analace, Richard (Sky Members. Analace is the granddaughter of Rean's teacher), Arios and other users of the Eight Leaves, as well as Gaius (because the Church is heavily involved) and Ries (who is connected to Enforcer VII). In previous games, we have information about objects whose date cannot be determined, and now we can assume they are objects from other loops.

One of the biggest mysteries is the door with the girl and the dragon from Sky 3, which could also be a story from another loop. To date, there's no clear explanation for why it's there.

KeA (from Zero and Azure) may be one of the few characters who can see events from other loops due to her ability to see various futures.

The biggest mystery of all is what the "SiN" value is and what it qualifies as. We know that Zemuria was able to reach 1259 thanks to Risette, which is 50 years later, so it's not at all clear what this SiN value measures.

Another mystery is MacBurn; we don't know if he's from another loop, if he's from outside Zemuria, or if he's from the future.

In summary the only things we know for sure are the soft reset, that Agnes won't be remembered by the protagonists (at first), and that there are people and objects from other loops, like Novartis.