Well, being that Cotto made Sergio sign for a 159 catchweight and came in at 155, I'd expect they would settle on a catchweight somewhere between those two numbers. In this case the WW titlist would dictate terms in negotiations to the MW champion, just as a former JMW titlist dictated terms to the MW champion when Cotto won the belt. The man who brings more money to the table has more power at the negotiating table.
Im sure he could be more then competetive with many of them. Only ones at the moment I would favor over him by a wide margin is Golovkin.