I made a topic about this a while ago when the V21 shadows and shaders idea was recently released, but now that we have shadows and shaders, I thought it'd be good to resuggest it.
This would be like the spray can, like have it's own row similar to fx, that would change the shininess of the brick that is painted, to give the illusion that it is a different material. You could paint a brick gray, then texture it really shiny to make metal, or make an offwhite wall then paint it the least shiny, to make a stucco or matte finish.
Discuss/make.