While I have questions about how often this would be useful (hidden line works fine for us), this seems easy to implement and doesn't add much clutter to the interface.
I once did an exterior elevation with different colors of stucco. On the construction document sheet (Hidden Line view), each different material had a foreground stucco fill and a background solid fill, and the background fill changed shade for each color. For the colored elevations in the project (Consistent Colors view), I had to override the wall category to hide background hatches so that the background fills didn't cover up the surface color of the material.
I would probably still use this workflow even with the proposed "Consistent Grayscale Colors" option for fine-grained control over contrast, but "Consistent Grayscale Colors" would give me something workable much much faster with fewer gymnastics.