If cotto were to somehow beat GGG I'd be willing to bet Floyd would try him at 160 to get that middleweight division assuming he gets past pac. GGG also on record saying he's "not a big guy" and could come down to 154. I don't think anybody including Floyd wants any parts of this dude at 154
GGG probably can make 154 but with some discomfort, otherwise he would just campaign at 154 as his regular weight. The reason he'd be willing to do it is for a Superfight. Cotto just needs to fight anybody right now he's been out of the ring too long.