Despite the fact that the next mainline entry in the Kingdom Hearts series will wrap up some major story beats for the franchise, this isn't the end of the Square-meets-Disney universe.
In an interview with the LA Times, KH creator Tetsuya Nomura emphasized the fact that Kingdom Hearts III will not mark the end of a trilogy, but rather serve as the next chapter in what will hopefully be a long-running franchise.
There was never a plan. As a core game, this is finally the third, and 10 years have passed. I couldn’t call this a trilogy. There have been so many spinoffs.
In ‘Kingdom Hearts 3,’ the battles that the characters have been fighting for the past 10 years will come to a conclusion. That is the plan. But the series will continue. Only the particular enemy they have been fighting the past 10 years will come to an end.
Kingdom Hearts III will be coming to both the PlayStation 4 and Xbox One at some point in the (hopefully not-so-distant) future.