Arihiko+Nanako combo would be pretty amazing. I still say they should add in more unknowns from the Tsukihime lore, such as other Dead Apostles or Lorelei from the Magic Academy or someone else from from the Church executioner squad. (of course, what I'm really requesting is loli Altrouge)
But really, considering that they're already adding in 3 expected characters (both mecha teams and neco chaos) and 2 brand new characters (lolazaka and ryougi)...they're prolly not gonna be adding in any others. Plus, the only unlockables they've ever had in the past were just joke charas who weren't even worthy for their own space on the chara select screen. I'm not expecting anything new in terms of characters.