The Last of Us: Part II’s Trophy list has been updated with two new trinkets to unlock: Grounded difficulty and Permadeath. This suggests that an update is imminent, adding the enhanced difficulty options. The title hasn’t been patched since around launch, so Naughty Dog has clearly had this cooking for quite some time.
It’s worth mentioning that the two new Trophies are separate from the main list, so you won’t need to complete the game on its hardest difficulty in order to unlock the Platinum. We suspect more information will be revealed in the near future.