[SPOILER WARNING + MINDBLOWINGLY AWESOME WARNING]
This is the secret clip that plays at the end of Kingdom Hearts II Final Mix (only in japan), which is a continuation of the one at the end of the American game. DO NOT WATCH IT IF YOU HAVE NOT FINISHED KH2, OR ARE NOT INTERESTED IN KNOWING ANY DETAILS ABOUT THE NEXT GAME IN THE SERIES.
I've also read a short interview where Nomura states that, though this game is in the KH universe, it is not KH3, but instead the first (of potentially several) in a new series based off the KH franchise. Also it seems that this is his current focus, meaning Final Fantasy Versus XIII has been unofficially delayed. Since it never had a set date, I guess it really doesn't matter.