what happened to volumetric lighting / fog

I get that, but you need to realize that just because it worked for one game, doesn’t mean it will work with all. You’d have to “dissect” the rendering engine to see exactly where they bump graphics up and where they tone them down. Which ultimately boils down to game art direction. Some developers might be fine with sacrificing high res complex shaders, or complex AI, if it means being able to turn up the dials on things like atmospheric rendering. The point is that detailed volumetric lighting has a pretty high cost on frame time.

Here’s a good write-up of making a volumetric raymarcher in UE4:
http://shaderbits.com/blog/creating-volumetric-ray-marcher