Pixel count is just a small portion of photorealism, and we can certainly notice a lot of difference from the models at fullHD from game to game. Just compare the facial model between three great games like HZD, UC4 and Detroit. You'll still easily see how much better Detroit is and they are all rendered at similar pixel count.
But geometry, polygons, texture, and several other effects are still improving a lot. Don't worry when gen 9 really starts to blow you'll be able to see the difference to Killzone or Infamous Second Son.
Yes PS3 to PS4 is the peak evolution, we still can see the difference. But from PS5 to PS6 onward , we will just be seeing increasing of resolution and performance , the rest of the hardware probably will be focusing rendering the amount of object or character in one area.
If you want to see the end goal of photo realism is, just look at FF7 remake character model that has the same quality with the CG model in FMV CG scene or Resident Evil 8 in game model character which already using photo geometry using real human model
I don't know what else we can achieve beyond realism, current gen can already render realistic model with the exact same features . What only lacking this gen is proper lighting (Ray Tracing ) and animation and also proper physics and simulation .