Isn’t there some ROTS concept art of Grievous where it’s clearly Maul’s eyes behind the mask? Someone at ILM must have at least thought about the idea, even if George never did.
Are you thinking about this one?
(This was the highest res. one I could find.)
IIRC, it was some ROTS banner which featured a crude CG Grievous figure with Maul’s eyes. It was posted somewhere on this forum years ago.