I agree, and I don’t know how I would approach it. I’ve been waiting for nested dielectrics for a few years, but I guess things just takes time. Luckily I don’t have to deal with it at all for my regular render stuff.
But for simpler stuff, like showing partially wet dark bumpy rubber where the specular defines most of the visibile surface structure, I would just lower the specular where it is wet and call it a day.
Correct. You shouldn’t use any regular surface shaders with the Principled shader, unless you only want DisneyDiffuse and do the rest manually. Principled is supposed to create physically plausible materials (not that it does because it not only breaks energy conservation - but adds energy, but that’s another story), not physically correct ones. It’s purpose is not to replace all other means of creating materials (especially transmissive/translucent/thin ones), but a quick way of getting 90% of them done easily and without horrible mistakes. Having it available doesn’t mean you shouldn’t learn the manual ways. It’s only a tool. A multi tool, yes, but not a tool that does everything.
And I did ask for a mixing factor (roughness affected fresnel) and specular color output for the principled should it come in handy, but I wasn’t heard. The point of that was that Principled doesn’t produce the same output as we do when we do the simple “reduce fresnel by roughness” in our own PBR setups.