I re-read my previous post and realized it is a bit fragmented -- maybe not so easy to understand what I'm getting at.
ThinSSS and AGS both work well for single thickness surfaces -- on an infinitely thin polygon... which is great for ease of use. However no infinitely thin plane exists in reality to my knowledge so the very foundation that we are developing on is flawed.
Then you add into the equation compromises for poly count like smoothing angle which approximates a smooth surface where none exists and we are working with a foundation for our materials that bears hardly any relationship to how things actually are in reality.
So you
could say the materials are unrealistically made, but the reality is they are conforming the pre-existing rules of the substrate they are applied to... therefor they can by definition never really be realistically designed.
I find it odd that we work in a 3 dimensional medium with ultra 2D parts (polygons) -- which is why I think Voxels make a bit more sense... they have 3 dimensions themselves and therefor are already that much more 3D.
I think if you look at particle simulation (like Realflow) you will see the future of the future in 3D -- after all everything is just made of particles in the real world.
Unfortunately I see the reign of the polygon as being very strong and so my hope for the immediate future is that more powerful material systems will lead the way into our particle based future.
One example I can envision is a much more powerful displacement system that would work like the thickness map in ThinSSS but by generating actual volume at render time.
A dream now, but technology does not sit still... so maybe soon.
Best,
Jason.