During Japan D23 a brand new trailer was revealed officially showcasing a Monster's Inc. world, the trailer also includes footage from Toy Story and Tangled including past Kingdom Hearts characters such as Marluxia and Vanitas (plus Ariel summon!)
In the second trailer it premieres Utada Hikaru's new song for Kingdom Hearts 3 "Don't Think Twice" the trailer also shows off Riku and Mickey's new look for the first time.
Also according to the people that were at the event the official release date will be announced during E3 so keep a lookout for that!
SOURCE 1 & 2
Edited to add the English subbed trailers :)