I think it would be a cool idea to implement a toggled LINE OF SIGHT difficulty options as an Update/DLC, available in any dificulty level.
This would bring about an intense first person experience while in third person. You would have to further rely on sound and play in higher tension atmosphere. No more using the cam to look around corners and behind you to cheat, you need Sabs to face what you wants to see. For example, You might want to check your 6 if you hear something...ha turn around and wham an enemy appears mid swing right before sabs line of sight.
Sub categories like environment, enemies, items, traps that can all be toggled on and off separately. So if you want items only visible at all times you can.
Environment: toggled on would be for the hardcore players. Environment out of Sab's front field of view will not be visible to the camera.....leaving you with a void/white noise visual/fog or visual style not in Sebastian's peripheral. Toggled off and environments will remain fully visible, leaving the Fog of War option selectable.
Fog of War: toggled on will effect new areas Sebastian has not laid eyes on before the cam does. Once revealed the surrounding environment/level will remain visible unless the Environment toggle is selected, which would prevent Fog of War mechanics from being enabled. Dying will reset Fog of War of course to last sav/checkpoint.
The rest like enemies(including their shadows), items, traps can have Fog of War traits as well. Once revealed by Line of Sight can remain persistent out of Sebastian's peripheral or adhere strictly to Line of Sight mechanics.
This along with the other propsed Checkpoint option/toggle would ramp up difficulty and add to the tension/atmosphere.