1st this is nowhere "amazing-looking", animation work is good, effects are good but environmental detail is pretty bad. It's all very platinum, definitely not a game that you would play for its graphics.
Then to me this not open world, at least not open world in the sense of say MGSV, ubisoft-game or horizon, this is a multi-route game but it has clear barriers as to where you can go so for me it doesn't fall under that category.
I dont see any reason why this couldn't hit 1080p on regular PS4, even if its like other platinum games and it strongly drops fps (although it goes mostly unnoticed thanks to an acceptable framepacing).
I'm not saying this is all Sony pushing for the new hardware, I dont believe that at all, but I do believe that having to work on two versions has probably take off optimization time from the PS4 version.
This is ridiculous, the only reason we dont have more of these is because no dev targets 60fps, not because the machine can't do it. And if anything we dont have 60fps games because the CPU on these console are shit which doesn't have anything to do with resolution. You people try to look smart with your questions and shows you have no clue what you are talking about.