With as many games released between Kingdom Hearts 1 and the latest 3DS title, Dream Drop Distance, Sora's story still never reached a conclusion. When speaking with the LA Times, Tetsuya Nomura explained that Sora's story will come to end, but the series will continue.
With so many spin off titles for the 3DS, DS and PSP platforms, Nomura said that he "couldn't call [Kingdom Hearts 3] a trilogy." Regardless of the amount of games released in the past 10 years, Nomura described Kingdom Hearts 3 as the game to finish the lasting fight. "In Kingdom Hearts 3, the battles that the characters have been fighting for the past 10 years will come to a conclusion."
When speaking of the franchise, Nomura then added that after Kingdom Hearts 3, "the series will in fact continue. Only the particular enemy they have been fighting the past 10 years will come to an end.”
A few weeks ago, Nomura explained that without all of the spin-off titles between Kingdom Hearts 2 and 3, that people "people might forget about the game, might forget about the series.”
In preparation for Kingdom Hearts 3, you can begin to catch up on the story with the release of Kingdom Hearts HD 1.5ReMIX. The HD re-release will include Kingdom Hearts 1 Final Mix, Kingdom Hearts Re: Chain of Memories and Kingdom Hearts 358/2 Days. Unfortunately, the HD package won't include the second entry in the series.
Kingdom Hearts 3 will launch on the Xbox One and PS4.
Source: LA Times