It's not pushing it, if he calls himself TBE and ends up fighting Cotto for the MW belts at a catch weight. Of course that's just a rumour at the moment. But if that happens, there's no reason why he couldn't fight GGG at 154.
I don't see Golovkin having a problem making weight in moving down. He won the junior world championships at Light Welterweight and also won the Asian games in S Korea at light Middleweight. Murray is a good fighter it'll go the distance I see, unless Golovkin hits him with a great body shot, then it'll be an early night. I can't see Mayweather taking the fight, but it would be great to see.