Someone on this very thread posted a screenshot of Gran Turismo 7 trailer which states PS5 exclusive.
So, possibility #1 is, they lied, and GT7 was always going to be a PS5 exclusive. That sucks.
But possibility #2 is, in working on the project over the past year since we saw it, they re-evaluated the project and determined that a PS4 version could be produced as well (possibly with hiring a contract/subteam to do the porting,) and that financially, it has to be done one way or another since the market has had a tough year. So take out RT, create bakes of some of the light sources that was realtime GI, process a lower set of models, make some loading screens since you're going to need those now, and get to work porting down.
All we know is that a PS4 version exists. Everything about that version, and its impact on the PS5 version production, is speculation.
\And yes these games look nice but they are based on PS4 hardware. Your imagination cannot tell you how a true PS5 only AAA heavy bitter would look like with game design around CPU and SSD of PS5. Horizon I can already see the leaves looking static, no crazy flying mounts where you can rapidly travel around the map etc. I wanted to see something that cannot be done on PS4 not just a PS4 Pro 2.
Your imagination cannot tell you what a true PS5 only AAA heavy bitter would look like either. You're making up a version of Horizon where the leaves are super-next-gen and you can just jump on a flying beast to go wherever you want on the map (which A. would be a mess for level design if flight was just ever-present because PS5 could do it, but also,
they should be able to do flight even on PS4.) You'd be hard-pressed to name another game on another platform or on PS5 that is showing Horizon FW to be dated technology.
The actual game engine does what it does based on a decade+ of work at Guerrilla, with or without the existence of PS5, and the improvements they make for it in future Decima projects will be less about "the power of PS5" and more about just having more simulation algorithms to integrated into its toolkit. Decima is not a PS4 or PS5 engine, just like Unreal Engine 5 is not a next-gen engine or a past-gen engine or a mobile/Switch engine; it is an engine to make games, period.
I want to see something that cannot be done on PS4 too, but technology that really harnesses the power of these consoles in unheard-of ways is not on the market yet. We don't even know what those unheard-of ways are, even, if/when they ever do exist. UE5 is not done, and it will still have its drawbacks and "cross-gen qualities" when it deploys (and not just in cross-gen UE5 games, which will also exist; Nanite itself has distinct limitations that will make it not useable in circumstances and Lumen isn't a canopener either, so shiny new UE5 games will still mix regular models and baked lighting and you'll probably never notice the difference.) R&C Rift Apart is great and uses the SSD in a genius way, but it uses a lot of tech from Spider-Man MM so we're demanding new engines to qualify as next-gen, that game is out because it's "using a cross-gen engine." Then there's Returnal and Demon's Souls and All-Star Destruction and The Medium... those games aren't on past-gen, so they are what we have to go off of as far as "game design around CPU and SSD of [next-gen]", but you tell me, are they really what you were imagining when you close your eyes and dream about what next-gen is supposed to look like? Do you think those games all make TLoU2 or Ghost of Tsushima look dated?
Point is, what we're seeing on the market and coming up, that is next-gen right now. It'll get better, but I don't think it's the past that's holding us up. It's just really hard to do things that have never been done before, even with better hardware to do it with.