Here is my take on the matter from different perspectives:
And as I have previously explained many moons ago
Console perspective:
PS5 and PS5 Pro is still selling rather well.
Many more of you are still on the PS4 generation and have yet to move to PS5/pro.
Sony knows this.... PS5 family can still sell well for 2 or 3 years.
To me it looks like Sony might take advantage of that ,.and work on the PS6 to add more future proof features and functions, Ai and PSVR3 hardware...
It.makes.most sense to have an announcement release of PS6 for Holiday season 2029, and start 2030s with brand new PS6.
GT8 perspective:
Full Gran Turismo games are console drivers and sellers...it makes much more sense to me that GT8 should be a PS6 exclusive, maybe even a special package combo.
I want it that way and that would be ready to buy it, but not in two years, even if it released...
And then whenever PSVR3 is ready, I think 2031 or 2032 at the latest, they might even do another special GT8 bundle...
PD and Kaz situation
As much as we all want a proper 30th GT anniversary edition, I don't think Kaz and PD is realistically ready for it...
They could release something then, but it won't be worthy of a 30th anniversary edition.
They will release something for sure in 2027, but I doubt it will be GT8.
I can see a Spec IV with very extensive power pack for the 30th anniversary, and even before then, possibly end of 2026 we could see a second PowerPack.
Then GT7 Spec V to release in 2029 to allow some partial GTSport cross play with GT8,
And finally a Spec VI in 2033 as the final one to force everyone to upgrade to the PS6.
I can see longer life span for both the GT7 and PS5 family overlapping a bit with the GT8 / PS6 / PSVR3..
Times are rather difficult financially for a lot of people, people are tired having to update and update constantly... Let's have everyone on the PS5 family first, kill the PS4 generation, and only then can the PS6 show up
What about money!?!?

The single most important point for the developer.
As for money, looking at the good review of the latest Power Pack, I can definitely see at least 2 or 3 Power Packs release between now and 2030, to add revenues, and continue for the PS5 family of hardware being sold until PS6 can be polished.
I don't see the benefits of releasing PS6 in 2027....
From a technical standpoint, pS5 Pro is still very strong., even by then....
GT8 needs to be crazy good, especially with PSVR3 on PS6, and that requires a lot of time.... Which is not realistic for 2027, and barely even for 2030, but that makes most sense to me.