From what I understand it was a communication error. There is a Fire Emblem VA who voices an SC character.
I think I can address this now.
Yes, that is why.
And the character who shared a voice actor voices a character on both SC and FE.
That Soul Calibur character was one of the 4 that were most recently revealed, and a veteran character.
People should be able to deduce that fairly fast.
As for a guest character, I just wanted to say that the two most requested characters for Tekken 7's guest character were Kazuma Kiryu from the Yakuza series and 2B from NieR: Automata.
Instead we got Noctis. Because.... reasons?
I still think it had something to do with executive meddling on Square Enix's part and pushing him on Harada instead of her. Or they cut some kind of deal where getting him on Tekken 7 meant they could use 2B on SCVI. Who knows.
But I don't think anyone should be surprised if her success as a requested character for Tekken 7 paves the way for her being on SCVI.
No, I don't know at this moment who any guest characters are from my main and most reliable source, so this is not some kind of hint or stealth confirmation from me. But this is an important factoid to consider with Tekken 7's most requested guest characters, and how 2B was someone people against her inclusion were only against her because "she'd fit better in Soul Calibur."
Oh if they only knew Noctis was awaiting them on the other side as the choice at the time. lol