Just curious... does this new feature addition also involve texture changes, or is it really only the light and atmosphere that changes?
Neither actually. Inside the shader, you have (among other things) texture color of a pixel and light color as input, and you have to specify an output pixel color. How (or even if) you relate these things is up to you. Usually light and texture color determine the base pixel color based on a Phong lighting model which is then corrected for fog in the last step.
For the lightfield for instance, I discard the input light color and replace it by a position-dependent color vector which is computed inside the shader. You could do very weird things with a shader, say an altitude dependent emissive glow, or a fog that whitens out close objects and leaves distant objects unaffected...
For the dust effect, I modify the base texture color before passing it to the lighting equation. For the snow effect, the base texture color gets replaced by an alternative snow texture based on altitude. I've actually been thinking that it'd be nice to have an autumn-colors effect based on a hue rotation of a forest texture. What's keeping me at the moment is that it's complicated not to do this for needle forest at the same time, and that my non-GPL forest textures may respond to the rotation in a different way than the default textures.