HOW IN THE HELL WON'T IT BE POPULAR? Almost every gaming freak in the WORLD has a 360. It's the second best-selling seventh-gen console, behind the Wii. And no, it won't kill the KH series. In my opinion, it will expand the KH series popularity.
And it's an amazement that you people keep saying that it will never happen on 360. That's what people said about DMC4 and FFXI, and look what happened. (Even though FFXI sucks.)