It has occurred to me the material system is a bit complex. One of the first things you have to figure out is which of the various material you need to use to suit your purpose. If you know the materials that's not a big deal but if you decide to switch between them - ie, you started with a matte but now you want to add gloss or translucency it can be a bit of a hassle.
Anyway, its not a big deal, but a number of the materials could be condensed into a single material which might simplify it a bit.
For example, from what I can see the mirror, matte, matte translucent, glossy, rough glass, glass etc could all be combined into a single material like the glossy translucent.
For instance, the current glossy translucent can mimic most of the base materials. If you added a refractive component below the diffuse, and possibly a volumetric component then what other materials would you need? Of course internally it would make sense to optimise special cases (like matte, mirror, glass, etc) but from the user point of view you'd just be playing with certain components, rather than different materials
I don't have time atm to work on it but I was interested in what other people thought about the idea?