Not sure what they would improve (besides gameplay) for a PS5 remake, Japan Studios I don't think would care much on making it 4k60fps (but sure they could hire a studio to do it).
Yep, from all the posts here seems like the gameplay needs a great overhaul.
The game had quite a bit of slowdown, even on the pro. It was also a bit blurry at times with not so great anti aliasing. The frame rate drops made the game seem more clunky at times than it actually is. The gameplay doesn't need a great overhaul, it needs consistent 60 fps to back it up. One thing they could improve is the speed at which boy walks / runs. There should be something in between snails pace and brake your neck over every obstacle sprint pace.
After seeing how good SotC can look with HDR and pristine sharp visuals, TLG could use some of that love as well. I still have this as my background on ps4, in game screenshot looking better than the box art. It looks even better with HDR :)
The last Guardian forest