People were kidding themselves if they thought the project was going to continue to include the PS4 going forward. It’s realistically a 10 years long project, if not more. Yet I see some people getting mad at Square Enix for moving on to the current gen with the project.
With how the scope of the story and gameplay opens up once you leave Midgar, I cannot fault the developers for not wanting the project to remain tethered to a console architecture that would become a headache to develop for in order to make their vision fully realized at the quality they want the project to be.
I was actually expecting cross gen due to SE looking how it can make the most money and shooting forward with development with calibrating for next gen. So targeting fall 2022 and simply using current working assets as they done in past FF sequels (X-2/XIII-2). Then they'd essentially port up to PS5 (4k/60fps/better textures & lighting). But its true that Part 2 will demand much more in terms of open areas, in the long term it may save them a fair amount of development cost by dropping PS4. Square also want the mainline series to be cutting edge. I've also been surprised by how quickly new gen software sales has overtaken last gen (at least at launch, Hitman for example), by the time it releases (fall 2022-2023) the market for PS4 software outside of Fifa & online service games will probably be dead.