I'm no developer, but this seems like one of those Gamer Questions that betrays a significant lack of knowledge. Setting aside the assertions in here that TLOU: Pt2 looks dated (WHAT), the idea that their games have to look a certain way "because the engine" is bizarre to me. Do you think the engine makes the art?
For the love of all that is holy, I hope they don't find some need to scrap everything they've built to this point. I would love to see another Naughty Dog game within the next five years, but I don't want to break any of their employees' backs to get it. It's just so strange to me to observe one of the best looking games ever made, which also happens to be as mechanically polished and pleasant to control as anything on the market, and think "ehhhh, engine's kinda dated, huh? Need to slap a new engine in this bad boy."
Maybe they should change the exhaust too.