Here are the components of the shading:
- Diffuse lighting
- Soft shadows. Used instead of ray traced shadows. Also eliminates the need for ambient occlusion.
- Subsurface scattering (so called). I figured it looks more like effects of depth volume rendering, not quite like subsurface scattering, but can account for some types of a similar effect.
- Fog. Mainly used to hide numerical errors for large distances. Instead of light blue (or other fog color), can be set to black to simulate view-aligned lighting.
Here's the current output: