I really hope that the differences between the PS4 and PS5 versions are solely graphical, and there aren't any discrepancies in content or game mechanics. Not only is it still hard to get a PS5 at the moment, but I also don't think it'd be even worth spending about half a thousand dollars on a new console just for one game.
I think PD made a very smart decision making GT7 also available on PS4, as I think limiting it to the scarce PS5 would hurt sales. If the differences between the two versions truly are solely graphical, then I think that'd be fantastic for sales. But if there are differences in content and game mechanics - especially in post-launch support - I think there'd be an outrage. But I also recall them saying that they plan for both versions to have cross-play, so I can't see that happening if there's going to be a discrepancy in content or game mechanics, with dynamic time/weather being an example of the latter.