I don't think so. Remember they are still busy with Re:Mind. The development for the next game will not start until after Re:Mind is released, and it's confirmed for this winter... PS5 launches by the end of 2020 and that would leave less than a year for Squareenix to develop the next game, that's a very short time. I know some of the non numbered KH games were developed within a year or two, but a game with KH3-like graphics for PS5 would need much more time than that, even if they reuse assets. And they would have to learn how to use the development kit for the new console and that requires some time, too.
Judging on how they release and develop KH games it varies on the game, usually it's 1-2 or 3-7 years for a new KH game (depending of the KH title). For the first KH game, development started in the year 2000 and ended in late 2001/early 2002 (Jan./Feb. 2002) which made it 2 years of development.
Kingdom Hearts II started after the release of KH Final Mix in December 2002 until 2005 (2 1/2-3 years).
Not sure how long development for Chain of Memories, Coded, and 358/2 Days took.
For
Birth By Sleep, development 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.
I'm very curious for how long it will take to develop the next KH game cause they still can reuse the character models and assets from KH3 without restarting from scratch again as they are using the Unreal Engine 4, but 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 KH game for the PS5 to come out around 2021 or 2022, mainly the latter as it's the 20th anniversary of the first KH game and the KH franchise.