It may be a little premature to say that Kingdom Hearts 3 has a release date, but Best Buy isn't one to care about the fine details. The retailer has since put up a pre-order page for Kingdom Hearts 3, dating it (incorrectly, I might add) as a 2013 release, no doubt put there as a placeholder. Check it out here.
Interestingly enough, the pre-order page has a box cover art of Kingdom Hearts 3, which may be of interest to anyone looking forward to the game. The artwork itself is a placeholder, and appears to be official, though the box art is most certainly far from what you can expect to see on the final box once the game is properly dated and announced for release.
Kingdom Hearts 3 was announced at E3 this year and gameplay elements were showcased at Sony's E3 presser, where the game was confirmed for release on the PlayStation 4.
It should be noted however that the game is—to our knowledge—not a PlayStation 4 exclusive and that it will also be released for the Xbox One.
We'll be sure to post an update on the game's real release date once Square Enix releases that information to the public—and to us.