This definitely looks like that using a LDraw file as a source image ia a good idea, as it solves several shortcomings of current implementations (eg. render of metallic paints).
...and a related idea: the LDraw pattern used as image does not need to be flat. Not only it can be layered, simplifying the drawing process (as already tested by Roland), but also formed! I think that we could very easily "convert" many existing 3D patterns (eg. the minifig heads) to use the new specification. Legacy renderers would still used current formed pattern as fallback, the new ones would apply the existing pattern onto the raw shape, eliminating the crumbled pattern effect and allowing for clean primitive substitution...
...and a related idea: the LDraw pattern used as image does not need to be flat. Not only it can be layered, simplifying the drawing process (as already tested by Roland), but also formed! I think that we could very easily "convert" many existing 3D patterns (eg. the minifig heads) to use the new specification. Legacy renderers would still used current formed pattern as fallback, the new ones would apply the existing pattern onto the raw shape, eliminating the crumbled pattern effect and allowing for clean primitive substitution...