The title says it all.
Here's my guess of what will happen:
It should take place 5 years after United As One (matching the release date).
- The Human-Garde at the Academy, possibly Walker too, will be the narrators and the primary focus of the novels. Nigel, Ran, Caleb and/or some new Human-Garde characters will be the narrators (I don't see Daniela getting a narration; she already had one)
- Nine and Lexa will have big roles for sure (cause they're training them at the academy), but will not be the main characters.
- Adam, Rex, Sam, Six, and Malcolm could have semi-major roles. I don't see them having narrations.
- Ella and Number Five will likely have more minor roles, but I'm sure they will still be in it.
- I don't know where I see John and Marina. Also I do hope that John x Marina does not happen. That would ruin the memories of Sarah and Eight.
I hope they tie up these loose ends:
- Why the humans were given Legacies
- Doctor Zakos
- Adam's mother
- The Pendants
- How Pittacus got to earth/how he wasn't prepared when Setrákus invaded Lorien
- One's Body
I don't think the mysterious caller or Six's chest will be addressed, as they haven't been addressed since Power of Six, prior to the changing up of the authors.
Of course, this is all speculation.