In a conversation between Mad Scientist and Gamerboy, Mad Scientist has said he wants any long term relationship he's in to be nonmonogamous. So at least he's not totally against the idea.
Like you said, any conversations we have had about alternative relationships have all been hypothetical.
I understand what you were saying about the fear of putting yourself out there and possibly risking offending him or loosing the friendship. This is a regular thought of mine too.