If the architecture could easily have been utilized by the PS4, I imagine you would have PS3 BC out of the gate Whether this means less remasters is debatable since a remaster would, theoretically, be better looking and more content complete. Like, I think TloU Remaster would still be a thing because it essentially acts as a 'GoTY edition'.
In fact, I imagine a similar thing will happen with PS5 (and XSX maybe?). There will be remasters but they will basically be the complete edition of the game, so FF15 with all content or KH3 with all content in a single package etc. While the content itself is not exclusive to next gen, that particular release will be.
Just my thoughts
After CDPR announced that people who buy Cyberpunk on current gen Xbone get the XSX upgrade free, I hope it pressures other publishers to follow suit and not make us buy games twice. I’m sure Sony has a similar plan in place.