Cleverly is VERY big compared to GGG. Weight classes exist for a reason. Is it possible? yeah sure why not, but I wouldn't bet on a GGG win let alone a GGG ko.
Golovkin is a normal sized MW and has never fought outside that weightclass so I wonder what makes people think he would do so well two weight classes higher. If he was comfortable with fighting guys who would clearly react better to his punches, I would assume he would go for it as his own division is essentially dead now.