Though we doubt anyone was looking for it to come out TOO soon, Square Enix advises folks to manage expectations when it comes to Kingdom Hearts III. With Tetsuya Nomura directing both that and Final Fantasy XV, it's going to be a while before the Disney/Square collab continues.
Kingdom Hearts producer Shinji Hashimoto spoke with IGN, explaining that they "can't create these two big games at the same time… It's a difficult job, as we want each game to be perfect in terms of quality." It seems the whole reason Kingdom Hearts III was announced so early was to reassure people that it exists in the first place.
On that matter, Hashimoto said, "A lot of people have wondered for the last couple of years if Square Enix has actually been working on Kingdom Hearts III; that's why we announced it at E3 this year … But please, we need you all to understand that there's a lot to do."
In other words, we hope you're really patient. Kingdom Hearts III is in development for PlayStation 4 and Xbox One, and will pick up right after the events of Dream Drop Distance.