To me the future Djoko - Nadal matches will come down a lot on Nadal's serve.
I know Rafa serves slower on clay, and yes his serve tends to go haywire these days a little too often. But against Djokovic, unless Nadal has a good serving day, he's at a massive disadvantage. On any surface. This is almost regardless of Djokovic's level. He got clobbered on his second serve today winning just close to 30% of the points. If you get pushed on the defensive immediately when you serve, always keep on struggling to hold - it's just massive pressure.
Of course, Nadal probably won't get his 2010 serve back. But his serving this week, has been abysmal to say the least. He might be able to get away with it playing others, but not Djokovic. His team has to figure out a way to have a consistent first serve that enables him to have the ascendancy in the rally, as well as win cheap points. It's more complicated because he cannot have a very low % - as then his second serve gets exposed. He definitely needs more pace. Serves under 110 mph won't cut it IMO.
Djokovic actually came down to earth in the 2nd set. He wasn't at the Rome 2011 Final level for instance. Otherwise the match might have been less closer.
Rafa has his work cut out. He can definitely get better, and probably will. But RG is dicy for sure. He has to get one win over Djokovic before that, otherwise it might be a tough ask.