In a post to Twitter the official Kingdom Heartsaccountannounced the release date, along with debuting a short 10-second teaser. We still might perhaps get some more gameplay at the conference though, so it might be time to get your hopes up.
Franchise director Tetsuya Nomura took this announcement as an opportunity to apologize for the delay, but promised that more information and new trailers would be released during the Square Enix E3 press conference on Monday, June 11.
A trailer released at last year's D23 Expo reset expectations for a release sometime in 2018, though we'll have to wait longer to see the likes of Big Hero 6 and Wreck-It Ralph join up with Woody and Buzz. Kingdom Hearts II came out in 2006.
No mention has been made of a release of the game on Windows PC, but with the recent porting of Square Enix's Final Fantasy XV, it's not necessarily out of the realm of possibility. Seriously, Kingdom Hearts 3 has no right to look his good.
Nomura has noted that the game will have another playable character besides Sora.