While there has been some speculation via datamining to suggest that Setsuka will become DLC at some point, and thus some may render any further speculating moot, however I would note that curiously there have been no mentions of Setsuka at all either in the Soul Chronicles nor Libra of Souls. In the case of other DLC characters (excluding Tira (who was a Pre-order bonus) and the guest DLC characters) Amy is in both modes, Cassandra appeared in Sophitia's Soul Chronicle, and Hilde is mentioned as part of the "Taking on the World" Side quest. However, the "Second Samurai" side missions involving Arthur have him mention having a daughter (of which as far as I can recall had never once been mentioned in any prior game). Also amusing to note that Arthur (a shipwrecked Englishman who learned the way of the Samurai) and Setsuka (who is of some unknown European descent) are both naturally blonde-haired. Is it possible that a retcon will done in which Setsuka would be established as being Arthur's daughter? If so, it would be interesting if that some done.
Meanwhile, though there has been nothing at all to suggest, neither by mentions in Soul Chronicle or Libra of Souls nor datamining, that Z.W.E.I. is going to be appearing in SC VI, but Wilhelm von Krone's character entry with Soulcalibur characters index on TV Tropes.org (and for disclosure, I'm also a part of that website's community) includes as part of his character entry (here for those interested https://tvtropes.org/pmwiki/pmwiki.php/Characters/SoulCaliburOtherCharactersNewTimeline) that suggests some sort of connection between Wilhelm and Z.W.E.I. (possibly that the latter becomes a new identity for the former in some way). If Wilhelm is one and the same as Z.W.E.I., might it be possible that the Wolf spirit that Z.W.E.I. has is the spirit of Wolfkrone's founder?
Okay so what do you think of these speculations I have presented here?