Of course it'll never happen. Cuenca has been on American television once and has no kind of name. The "50-0 on the line" angle does kinda sell, though.
He should've paid his sanctioning fees at fought Kell Brook at Wembley for his 49th fight. That way, the winner would become the first man to unify all 4 titles at 147 since there was 4, and it would've also been Mayweather's first fight outside his back garden. All the great fighters have traveled outside their comfort zones. Then if he won, for his 50th he should've fought the Canelo-Cotto winner for the lineal title in a 6th weight class... ...but he fights Berto (he would've lost to Special K anyway)
The biggest fight in boxing right now is Cotto-Alvarez l, if he goes for 50 he should fight the winner(preferably at 156+ for Lineal MW Crown.
Karim Mayfield. It would be one final FU to the fight fan. I think if Rod Salka can bulk up they could do a catchweight around 145 pounds. The undefeated Aussie Cameron Hammond is also a possibility. He's not well known but it would give Floyd the opportunity that he could sell 2M PPV buys with a relatively anonymous B Side. He's already rated by the WBA, where Floyd holds a belt, so the sanctioning bodies wouldn't block it.
Cotto vs Alvarez winner at 160 or Pacquiao rematch. All the rest will be considered pointless in comparison to those two.
They're now trying to sell the Berto PPV as Floyd's farewell fight, so if they're on the level (were they ever) there won't be a 50th fight.
It will be Pacquiao, or the winner of Cotto/Canelo. I doubt he takes another soft contender after Andre Berto. I could be wrong though. lol
I know Pacquiao has an ATG resume but I wouldn't like to see him given a shot straight away after his May performance.
I would like to see a Pacquiao rematch if they're certain that his shoulder is 100% this time. That's the most competitive fight out there. Obviously Golovkin would be fantastic but I cannot see Mayweather taking that fight in a million years.