Interesting link, thank you!

It looks like a good model for lower incident angles but begins to diverse at higher angles. There's also one huge caveat - it relates the GGX model to real world ground glass. Obviously it's important to compare like to like. However, very few materials in the real world are ground glass.

Looking around my surroundings, I see painted drywall, wood, paper, plastics, and textiles. It would seemingly be a mistake to assume each of these materials behaved optically like ground glass. I hope that similar measurements are carried out on other materials.

The same Cornell group has done more research in this area. Here is one for capturing the microgeometry of metals https://www.cs.cornell.edu/Projects/metalappearance/ Here's another paper from a different group on capturing the microgeometry using a lot of LED lights https://svbrdf.github.io/publications/MicroLightStage/Micros...

But I agree there should be a lot more work in this area!!