I bet the empty spot will be Adachi. Either him or Namatame. I really want another Persona 3 character though, any will work.
They already have all of my favorites so they can do whatever they want at this point.
Shadow Sho should be in the shadow section. I will be so angry if they waste a slot on another shadow version of a character.
I have a theory. If you look at the character select screen, there's still some empty spaces on the side. I think those are possibly more character slots and that we can move the character select screen and pick more characters kinda like Tatsunoko VS. Capcom.