Hate to say it but I agree with the babbling old man. GGG is a middleweight-super middleweight. Yea he can probably cut to 154 for weigh ins but he will be a lot heavier during the fight. Mayweather has gone up to super welterweight to face people before but it's really not his natural weight . Your basically asking mayweather to fight someone 20 pounds heavier than him with GGG. I think your trying to hard to find someone to beat him. He would be pretty disadvantaged going into that fight. It shouldn't happen.
Under normal circumstances I'd agree but it's Floyd after all, on the other hand if he were to lose it'd feel somewhat unfair it took a man much bigger than Floyd to beat him. Don't really know about this fight in all honesty, I'll say if it happens - great, if not then well let it be. There's no "ducking" or whatever involved if Floyd doesn't want to fight GGG in my eyes.