I doubt there is more money in the budget of PS to be able to afford another character from another IP, for the rest of the season pass it must be all the other characters that are popular, like Cassandra, Setsuka, Amy, Yung sun, Lizardman, and the rest which not really that popular. i think the most likely are Cassandra, Setsuka and Amy in that order( Amy is too young to be in but thats what was said about Talim too in the beginning so it can go everywhere from here on).
Amy is fine to be in, just on her age, because the story goes up to 1590, which is the same year of SoulCalibur II-IV. So she's not going to age more than a year between now and the end of SoulCalibur IV. The question is story relevance and if she's a fighter, which, originally, it was assumed that she wasn't trained until after the events of SoulCalibur II, since we were grasping at straws for story, but now, with SoulCalibur VI, we got clarity that Amy was trained in response to Raphael feeling Amy should be able to defend herself, and she does defend herself in both story modes, so... Amy is a fine inclusion.
Setsuka may have a unique fighting style, but she doesn't have story relevance, and that's her biggest flaw. She's so irrelevant to the story, that she wasn't even referred to in passing, alluded to, or anything. She has one line in a training article in the museum. She has less exposure than Rock, Hwang, and Li Long. That's not a good thing, unless they were intentionally leaving her out for shock value, but I don't see the point in doing that.
Cassandra is in, and she has a new design, but she doesn't fight, so that's her biggest argument against. Hwang, on the other hand, does fight, but isn't seen, so while he doesn't have a redesign, he does have a slight edge over her with regards to having storyline fights to participate in about which to tell a story that does involve fighting. Though Zasalamel showed us that not fighting doesn't necessarily mean you don't get a story. Only time will tell, really.