Square Enix's Tetsuya Nomura has confirmed that at least one Kingdom Hearts game will be released before Kingdom Hearts IV.
Fans who played Kingdom Hearts II when it was first released had to wait almost fifteen years before they could play Kingdom Hearts III, but it seems like the wait isn't over yet.
Square Enix has released compilation books for their games known as "Ultimania" guides, which contain concept art, interviews with the developers, and information on every aspect of the game. The Final Fantasy series has notably received many Ultimania books in the past.
The Kingdom Hearts III Ultimania guide was recently released in Japan and fans have already started translating the information and have released it online. An interesting tidbit about the future of the series was revealed by Tetsuya Nomura during an interview for the book, which has been translated and shared online by the Twitter page of the Kingdom Hearts Union podcast.
“As for the next Kingdom Hearts, there will be at least one KH title that will release before a ‘KH4’” #kh3ultimania— Kingdom Hearts Union (@khunion) February 28, 2019
It seems like the Kingdom Hearts series isn't over by a longshot, as at least two more games might be released in the future. Nomura stated that there would be a different Kingdom Hearts game developed before Kingdom Hearts IV.
Kingdom Hearts III sold a lot of copies when it was launched, so it makes sense that Square Enix would want to create more games in the series. However, the question is whether Tetsuya Nomura will be involved. Tetsuya Nomura is supposed to be working on the Final Fantasy VII Remake, as well as a possible sequel to The World Ends With You that has been hinted at, so it's doubtful that he will have much time to spare for Kingdom Hearts in the foreseeable future. It's possible that the series might continue with different creators at the helm in the future.
One thing that we can safely say for sure is that the next Kingdom Hearts game might have a dumb name if the other spinoff games in the series are anything to go by. Fans will have to squeeze as much enjoyment as possible out of Kingdom Hearts III in the decade long wait until Kingdom Hearts IV.