I can't really see someone like Reimu or Sakura being the Smash reveal. Persona might be a relatively obscure series compared to something like Final Fantasy, but Persona 5 was still a huge hit that was nominated for, or won, numerous awards and was generally considered one of the best games of that year, or even that console generation. By contrast, a character so obscure that it would make even industry veterans/developers/journalists go "who?" doesn't seem like a great choice for a reveal at the Game Awards.
I could easily be wrong about this, but it seems like the most obscure (non-Nintendo) series that made it into Smash so far were Persona and Bayonetta, and both of those were still considered game-of-the-year material and reasons to buy the system(s) that they were exclusive to. Something like Touhou or Sakura Wars don't really seem to have made waves like those series have, which seems like a big issue when the ultimate goal of the DLC is to get people to buy it.