Kingdom Hearts 3 is still in development over at Square Enix. Furthermore, we still haven't gotten a stoic release date for the title, which means that we may not get our hands on the game until late 2016. Considering that the game's first playable appearance has been confirmed to be at Disney's D23 Expo in August, it's still plausible that we get a late 2015 release. More information pertinent to the game should also be available at E3 2015 in June.
Until then, all we've got is the ability to speculate. However, one Youtuber – TheGamersJoint – has been doing a pretty swell job of guessing what sort of announcements and such will be coming out of the Kingdom Hearts universe. In one of his more recent videos, the personality states his case as to why Disney's Atlantis should be used as the backdrop for a world in Kingdom Hearts 3.
Atlantis was one of Disney's more popular releases, despite its movement away from traditional production routines at the company. The movie was innovative, well-animated and more mature than most Disney movies released before it.
You can check out the video below: