Before the official Principled Shader, we saw a few individuals engineer their own uber shaders with some effects that were pretty advanced for the early years of Cycles.
Ubershader v4.0 - New Release 5/24/2013, Come and Get It! - Artwork / Blender Tests - Blender Artists Community
UPDATE: Universalshader Fusion v2.0 volumetrics unified - Artwork / Blender Tests - Blender Artists Community
I have not tested the download links, but it would be interesting to see how they will look with things like AgX and true volumetrics and SSS.