I have to say, there is something more subtle in Naruto evolution that could take place and make sense as well. Communicating and properly being channeled with the Nine tails is what is required for Naruto to go to the next level. I think we got a taste of that when Pein hit him with a charka rod and much to his surprise and the girl next to him, he resisted while using Sage and Nine Tails mode.

I think that will play a huge part, while Naruto battles Sasuke and to make us readers impressed, Sasuke will start to dominate Naruto while he is in Sage mode, and then Naruto will merge the two, well three chakras including his own to form something greater and defeat Sasuke. Its my theory and I think it will be better then what the writer comes up with.