I feel like Skuld my secretly be the Master of Masters. I dunno... I just feel like a Valkyrie, who spirits people who die valiantly in battle to Valhalla (in Norse mythology, anyway), might also be someone who has eyes that can "gaze into the future". Or at least be someone with eyes that have seen a lot more than most have. Perhaps Chirithy is just exaggerating about how powerful the Grand Master is in the II.8 trailer.
Also, I know this is all Norse mythology, but I wonder... Do you think Nomura might try to bring some Christianity stuff into this all, too? If there are going to be three sisters (or at least a trio of three girls), he could possibly do something like the God, Jesus, Holy Spirit idea mixed in with all of this. IDK. It's just a thought.
Edit: I also think that the Player is a Xehanort vessel: the last one, probably. Perhaps the reason he/she never spoke before was just because he/she was an empty shell. But now- now Xehanort has capitalized on that fact, given the Player a piece of his heart, and that's why he/she's suddenly speaking.