Yes, you are right.

Photorealism in real-time by using PBR shaders looks very good. Especially I like these two scenes:
Youtube: .UE4 dynamic sun/sky test
Youtube: UE4 Archviz / Lighting

But as you can see, these levels are very small. And yet they run with a frame rate of 30 to 60 fps.
So doing a whole RPG with large outdoor levels and many NPCs is not possible with this technology.
I have to make a compromise. And my compromise is to refrain from intensive real-time calculations, wherever it is possible.

No, I will not recreate exactly the real environment. I only recreate small parts of the real environment. And these small 'pieces' will be cloned and combined to a much bigger game level.

And I will use a combination of ...

• ... real shadows from the original photos/textures (e.g. shadows of small stones, lying on the ground),
• ... pre-rendered baked shadows calculated with 3dsMax (for bigger shadows - e.g. for shadows of trees or buildings),
• ... and also some realtime shadows for moving objects.

You don't need all these things when lighting does not change in the game level. When you go into a forest making photos of all the leaves above you, then these leaves already look like they should look like. Then you don't need subsurface scattering and other things to make them look realistic. Because the leaves on the photos are realistic.

But you are right, in some cases it is necessary to use subsurface scattering and PBR and other things. E.g. when the leave of a tree is located at the eye level of the player, and the leave is placed in front of a light source (e.g. a campfire). But this will be used very rarely in my game levels.

, that's exactly what I was thinking when watching all this epic Epic realtime movies. Than I remembered that they already had a really cool realtime movie for Unreal 3 engine too iirc, and commercial games nowadays still barely reach that point (and that's only talking about the really looking ones). Anyway, interesting to see how this will work out.

Yes, you are right, in case of large levels it could result easily in bad performance. I tested e.g. this cool 2-sided foliage rendering with subsurface scattering, very nice how leaves react to turning towards or away from Sun, but in a large level (what I also need for my strategy game), it becomes slow on my PC (I'm just over UE4 lower end). Fortunately it is possible to use lod models and to apply different material for each lod models, and to use billboards for far models. And if you design the level to effectively use occlusion culling of the engine (avoiding seeing huge landscapes), it also can boost performance.

But the pre-made lighting and shadows do not allow rotation, so the level could be a bit repetitive, and too many assets would increase memory usage a lot (by the way, in case of an RPG level streaming is a good solution). Of course, not impossible, just seems to be a bit harder for me. Good luck, and keep us updated

, true but many commercial games I see have fixed lightning anyway (as in the lightning differs per map but no day-night cycle etc.). But ofcourse it could be a major pain change something afterwards.

it really differs if you bake lighting and shadows by the engine, or your assets already imported with baked lights+shadows.