@RagingGhost - Tira was not retconned in. Her backstory, as written, already set her up as defecting from Bird of Passage during the Evil Seed incident. You can say "retcon", but that's not really the right term to use, I don't think. Same with Zasalamel, their stories were written where they existed prior to their initial appearance, but they weren't created yet until SoulCalibur III, so when they reset the timeline in SoulCalibur VI, since we knew they existed before they were originally created as characters, it makes sense to see the origin stories that we could only read about before.
Talim is a special case, because she wasn't represented at all in SoulCalibur V (and neither was Zasalamel, part of why he returned too), but her story wasn't changed, since hers is the last on the timeline, it's just her quick origins before SoulCalibur II, nothing was changed to allow her inclusion. Cassandra would be the same, if she's in SoulCalibur VI, her story would just be her setup for SoulCalibur II, as she's not doing anything else in this timeline. Setsuka's timeline is a bit unclear without precise dates, so we might could see her training with her master before his injuries were dealt to him by Mitsurugi which would ultimately lead to his death which sets Setsuka's story up for SoulCalibur III, but it isn't really a certainty if those events are before or after SoulCalibur II, since Setsuka easily has the least story content of all of the characters.
But this is why I feel like Hwang and Amy have the highest chance, because they are foils and the other halves of two stories that we already have, in Seong Mi-na and Raphael. We would see the stories from their perspectives, with their motives and inner thoughts, and outcomes, which their endings would be extensions of the stories we already have. We could have Hwang's interactions with Han-myeong, being sent on his mission to track Mi-na, deciding to disguise himself, and after returning home, going back to the coast guard and setting up his next chapter where he could return for the next game. Amy, same thing, show her life as an orphan before Raphael, during, learning how to fight, playing her self-defense and training sessions, and maybe an event what was happening while Raphael's final chapter was happening from her perspective, to set up future events.
They really went out of their way to not show Hwang and Amy actually in battle, while they clearly had conflicts in both story modes. It's suspicious.