I think two new charas, plus Sagume, Kaguya and nue? can be plausible. Kaguya was going to be in a fighter(SWR, if I don't recall wrong) so it would make sense, and Sagume was the one responsible of all the urban legend stuff, plus she is the new book. The pairs in the story mode could be something like this: MariNito, Reishin, SagumexReisen, MokouxKaguya, Hijimiko, ichifuto, Koikoko, KasenxSuminerdko, the two news, Maminue.
tl;dr some fandom favorites return in a plottwist no one could see coming, like Kisune, Tokiko, Kosuzu, that kappa that appears in WaHH and a new one. After tanned Cirno being the champion of Summer, nothing will surprise me anymore.