First of all: The matlib is a great addition!! Will definitely help even advanced users if made right.
Critique/suggestions:
• Real world scale is necessary.
• Triplanar mapping should be used for all bitmaps.
• Avoid making lots of materials where color is the only difference. It clutters the matlib, and having a CoronaColor-map/Multimap to change the base color to whatever suits your need is better.
• I see little use for materials with small bitmaps. Making a texture that only looks good on the shader ball, but not on a 3x3m wall is pretty pointless.
• Making "wet" and "dy" variants of common exterior materials would be great. (Pavement, concrete etc)
• No "Pilsner" shader?! Come on!