Unless they add 4 more chars to make it a symmetrical square then I dont think they will add anymore characters
So much for SHIKI Arihiko or Touko :/
Well they could always change it so that you press the D button to switch characters, ala Chaos/Neco-Chaos.
I could see amber-mech and neko-mech switchable that way as well as akiha/seifuku akiha, etc.
Itd leave a few more spaces open for new characters. TM DID say that they would be adding "More mysterious fighters" or whatever in the Ryougi profile on the JP site. I for one don't find anything "Mysterious" about amber mech and seifuku, so logically, there is probably going to be at least one more "New" character.
Heres hoping for tohko. we need a puppet master character, and it'd make sense for her to be there if Ryougi is.
Shed probably just play like Liselotte on crack, with multiple familiars instead of one puppet. Which is a good thing.