New scans of Tales of Xillia from VJump magazine point to only six available playable party members for the game. It seems that way for now, anyway.
We have three new scans of Tales of Xillia from VJump. Though there's not that much new information or images, the scans do somewhat point out that there will only be six playable party members. There are other two characters somewhat introduced in the scans. You may be familiar with them from Rowen's character description — Droselle K. Schall/Char and Crayn/Klein K. Schall/Char, members of the Schall/Char family that Rowen serves under. The two are, however, not classified as playable party members.
The scans basically just summarize everything we know about the game as of late, like where the word "Xillia" was derived (from "Xillion"), the Chat Systems, the Double Raid LMBS, the characters, and so on.