Seriously, we're going to forget what Itachi said, and I like many others on the forums say, "Every jutsu has a weakness!" Damn, you think he was interrupted and meant "Every jutsu except my Susanoo has a weakness!" lol 
FRS, TBB, Itachi's strongest Susanoo jutsu together on a Chibaku Tensei that was just beginning. Maybe Chibaku Tensei isn't the ideal counter for Susanoo, and it's another jutsu, OK, but the point is that nothing is invincible. Nagato has the best diversity of strong jutsu to have one to counter Susanoo, so my answer is yes, Nagato could beat Susanoo. Without seeing it done, I can't prove it, I just believe it, and it seems logical. That's about as far as anyone can go with the argument.
Edit: Whoever called Psukkar a troll, read the forums, that's embarrassing.
Peace
FRS, TBB, Itachi's strongest Susanoo jutsu together on a Chibaku Tensei that was just beginning. Maybe Chibaku Tensei isn't the ideal counter for Susanoo, and it's another jutsu, OK, but the point is that nothing is invincible. Nagato has the best diversity of strong jutsu to have one to counter Susanoo, so my answer is yes, Nagato could beat Susanoo. Without seeing it done, I can't prove it, I just believe it, and it seems logical. That's about as far as anyone can go with the argument.
Edit: Whoever called Psukkar a troll, read the forums, that's embarrassing.
Peace