Well unless my information is incorrect, RJJ vs Danny Green is almost certain in the future, especially after Green's latest win. Anthony Mundine is probably fuming right about now.
Personally, it would be a hard match for me to watch. RJJ is a legend to me and Danny Green is one of my favorite boxers, and at least for the parts of Australia that still follow boxing, a hero.
As for the fight itself. I would say RJJ wins by a unanimous decision full of showman ship, however, RJJ is getting old, his speed is definitely not what it was, and Danny Green has improved leaps and bounds since his loss to Mundine. So IMO, I'm thinking if RJJ isn't careful, he gets KTFO'd by Green.