Ah I thought ninjas could only use a maximum of two different elements. If that's the case, then naruto should be able to create a minimum of two with the possiblity of more elemental rasengans. I can see how taking the time to create an additional elemental rasengan would disrupt the pace of the story but that really only applies to the current arc. In order to become a truly powerful ninja worthy of facing sasuke and akatsuki, he should exhaust the incredible potential of the rasengan. And time doesn't seem be an issue with his shortcut training. Just imagine, although unlikely of course, if Naruto creates nature manipulated rasengan for all 5 elements.