My skepticism of anything saying Mi-na will be in the game comes from 2 reasons that relate to each other pretty heavily. First is the perceived limited roster space. BN hasn't said anything about the final roster numbers for SCVI (that I can remember) but we seem to all be thinking around 23ish. The second reason is that, though Mi-na was in 2, 3, and 4, she's felt kind of like an after thought (to me at least, maybe others disagree) in those games. Just added to the roster for the sake of having a bigger roster because Kilik has been the long arms weapon user BN has really put work into keeping fresh. With those thoughts in mind why would BN use one of their limited roster slots on a character they don't really care enough about to keep fresh and unique?
Maybe I'm completely off base and just don't talk to enough people who play Soul Calibur outside of the Madison community but those are my thoughts. I would be very surprised to see Mi-na make the base games roster. It would be a nice surprise, I do enjoy the little I've played of her in SCIV and SCII, but it would still be a surprise.