The Pacman/Mayweather fight was much different, because those 2 guys are about the same size. They fight all the same people. I feel like asking GSP to fight Silva or Silva to fight Jones would be like asking either Mayweather or Pacquiao to fight Bernard Hopkins a year or two back, ya it would sell but it wouldn't make a whole lot of sense.
Honestly though, I think the odds of seeing the Mayweather/Pacquiao fight now is much higher since Pacquiao lost a few. Mayweather will get more money like he wanted, and he'll have plenty of film to exploit. If Mayweather loses his next fight or so (which I think is definitely possible since he really struggled with Cotto), can almost guarantee this fight will happen.
Zombie is born!