I don't think we can count summons as characters. Though the Luneth thing does bring up something I've been thinking about. I do have a theory that their may be more characters, they are just costume swaps for existing characters.

Cecil's swords are more like a lance if you think about it so I wouldn't be surprised if Kain was a costume change for Cecil. Bartz using multiple swords makes me think Gilgamesh... Its a cheap way to add characters into a game but it should please most fans at least.