I think it's something that wouldn't ruin the KH plot. Or even better, something that will advance it. Like somebody new. Oh, but that's never happened before. And there's NO POSSIBLE WAY that he isn't Xemnas or Xehanort just because of those weapons!!!!11!11!!11!!! Nope, not possible. Not even going to think of any single other possibility. I'm just going to ignore the fact that he seems to have the ability to manipulate time and not a single other person ever in the series has been able to do that before. I'm also just going to ignore the fact that Nomura really only used the Black Coat because he A] wants to hide his identity for now and/or B] hasn't even designed him yet. Nope. That's not it. He's an Organization member! Only explanation.