what about this idea …
the boolean modifier changes the intersected volume into a specific material . 
I like that idea. I’m not positive, but it sure seems like it would work.
What’s inconsistent is that the boolean tool (w key) already does this. That is, it takes the material of the object cutting/intersecting the one on which the tool is used and puts it on the intersected surface. Whereas the modifier counterpart does not. However, it does take the UV texture of the intersecting object, so using TexFace you can achieve a sort of similar effect if both objects have different image textures. Problem is, boolean sucks and sometimes doesn’t even leave you with a manifold mesh, that is, you end up with a mesh with holes in it, unnecessary vertices inserted at random places, and overall horrible topology.
