If they put Cassandra in, and Lizardman with a sword and shield as well, with all three of them having dinky little swords and shields, I'm going to effing cry. That's three slots used up with the exact same weapons, and entirely stifles CaS character creation options for me and others like me. As boring as Rock is, at least he brings a new weapon to the table.
MAYBE if one of the shields and swords were larger.
It has been brought up before, the size of the shields being bigger than they are, it would negate the idea of needing to crouch in order to block low, if it was a tower shield or even a bigger shield than a buckler that would cover a greater area. It's like, if it's going to be a sword and shield style, that size shield is about all they can really get away with to make it believable. And the swords that go with those shields, if the sword was a lot bigger than the shield, then it wouldn't be aesthetically pleasing. But the "dinky little swords", as they are, is actually about the right side for a gladius, which is what they are. Maybe if Siegfried's sword wasn't trying so hard to be Guts's Dragon Slayer and was a bit smaller, we could err on the side of realism a bit more consistently, but it is what it is.
SoulCalibur V having Patroklos style, Coward Sophitia style, and Malfested Sophitia style, though, I'd rather have had Patroklos style, Sophitia style, and Cassandra style, and that's probably about what we'll end up having in Lizardman, Sophitia, and Cassandra, should all three of them make it into the game. So even if it's not ideal that we have three sword and shield styles again (SoulCalibur II, III, IV, and V all had this, as a reminder -- III and IV, LIzardman had an axe, sure, but the premise is the same), at least it would be the most diverse set of three sword and shield styles we've had so far.
I think Cass is one of the most interesting girls in terms of personality and her sacrifice. I'm sure there's more they can do to diversify the moveset. I think she has more easy ties to the central characters as well. And in general, people often want as many female fighters as possible. It would be cool though if she comes back with a different weapon. If Aeon could do it in V, she could do it here.
It is possible that Cassandra finally realizes the longsword style that she was alleged to have planned to have for SoulCalibur V, but at the same time, if they were going to do that with her, then they could have had her using it in Lost Swords. I know Lost Swords was mostly a lazy cash grab effort of a game, and just used SoulCalibur IV assets for characters that didn't make it into SoulCalibur V, so it's not the strongest argument, but just for the sake of devil's advocacy.
Aeon had a plot reason to have a different weapon (in that he ate Kratos, which is ridiculous in and of itself, but...), while Cassandra's story would have her steal Sophitia's weapons all the same again, so I wouldn't anticipate her having a different style. I also wouldn't expect for her to have a story in this game, so she would be one of the "extra" characters, which puts her on the chopping block of possibly not making it, sadly along with Raphael and Seong Mi-na. Raphael does have a story to tell, but there's not really a place for him to fit on the list, unless the name under Grøh is Voldo and the name under Yoshimitsu is Raphael, but... I hope that isn't the case, since two games in a row without Koreans is... not pleasant.
They might could be DLC characters, perhaps, but they won't really shine in their stories until SoulCalibur VII, due to the constrained list of names we have in the story mode screen, assuming the list is complete (which why wouldn't it be if they bothered to blur the names?), they don't really have a spot to fit in. Keeping in mind that this game covers from the end of Soul Edge to the beginning of SoulCalibur II, it makes far more sense for them to save Cassandra for SoulCalibur VII, at least for plot relevance. We may -see- Cassandra in Sophitia's story, which would work if she's playable but doesn't get a story of her own, but she doesn't have a lot going on during these years to be active.