I see impossible to see Napoli being champion of the SerieA back to back, they never do something like that plus Inter needs to win something asap after losing it all in the end of the last season.
This plus this Napoli seems to be the best one and when this kind of teams are in that particular position they start to fall.
Napoli didn't play any European competitions last year and had a very advantageous fixture schedule. Inter, on the other hand, had reached the Champions League final and looked like a team that, with its tired players, struggled to qualify for both tournaments. The disappointing thing for Inter was their loss in the finals. They emerged from a very demanding fixture list but failed to win either the Italian league or the Champions League. As for Napoli, I don't know what they'll be able to do in these two grueling fixtures next year. I think their chances of winning the title are lower than last year.