I heard that the days game will be also about axel and gang finding out more about lea and isa's 3rd friend from the castle from the secret reports.
There also will likely be another spin off game with the Disney crew (Mickey/Donald/Goofy) visiting past worlds looking for Sora.
So expect many MANY spin off games before we actually get KH4. Likely wont come out till 2025+.
Or 2023, depending if it's ONLY 1 KH game coming out before KH4, cause Nomura previously said they were developing a KH title that is set to be released before KH4. Plus Square Enix is still using the Unreal Engine 4, and they can still reuse the character models (e.g. Sora, Riku, Kairi, Donald, Goofy, Roxas, Ventus, Aqua, The Foretellers, Xigbar etc..) and worlds (e.g. Twilight Town, Radiant Garden, Destiny Islands, Toy Box, Arendelle) from
Kingdom Hearts III for the next KH games without restarting from scratch again so development will move a lot faster than in previous KH titles. However when it comes to the new Disney/Original worlds and characters they create, it may take them another year or two to develop. I do expect the next new KH game that it's in development and coming sooner for the PS5 (or whichever console it's releasing) will likely come out around mid-late 2021 or 2022, mainly the latter as it's the 20th anniversary of the first KH game and the KH franchise and going by the release pattern on how they release a new
Kingdom Hearts game, it's usually 1-2 or 3-4 years for a new KH game (depending of the KH title) to come out.
Here's a breakdown for the development for the KH games:
- The first KH game started development started in the year 2000 and ended in late 2001/early 2002 (Jan./Feb. 2002) which means development lasted for 2 years. For Kingdom Hearts II, development started after the release of KH Final Mix in December 2002 and lasted until mid-late 2005 (2 1/2-3 years).
- Not sure how long development for Chain of Memories, Coded, and 358/2 Days took, but I think the former started sometime after the release of the first KH game and before KH2 entered Development.
- Development for Birth By Sleep started since 2005 and lasted until late 2009 (4 years), Dream Drop Distance started since early 2010 following the release of BBS and lasted until late 2011/early 2012 (1 1/2-2 years).
- Finally, Kingdom Hearts III had the most interesting development for a KH game, as development started since late 2012/early 2013 but due to a switch from Square's Luminous engine to the Unreal Engine 4 in October 2014, development for KH3 restarted under the new engine up until November 2018 (5-6 years of KH3 being in development (1-2 years under Luminous; 4.25 years under the Unreal Engine 4).
- Regarding the II.8 Final Chapter Prologue, I'm not sure when development started but I think development for that title started around the same time that KH3 switched into the Unreal Engine 4 (October 2014), even the Graphics from 0.2 Birth By Sleep seems to suggest it was the first KH title that the team were testing on and the graphics for this game looked uncanny when compared to the Unreal Engine graphics of the X Back Cover movie and Kingdom Hearts III.
Also, most new
Kingdom Hearts games usually are announced at the Tokyo Game Show (e.g.
Kingdom Hearts II,
Coded, 358/2 Days, BBS, the HD Collections and
II.8 Final Chapter Prologue), but their were some exceptions to this, such as
Dream Drop Distance (previously announced as KH: 3D) and
Kingdom Hearts III were announced at E3 2010 and E3 2013 respectively. It's possible we might get the announcement for the new KH games (aside from Project Xehanort) during the June Orchestra event/E3 2020 or Tokyo Game Show 2020.