Or how about not just a TBB rasenshuriken but a five element rasenshuriken.
Think about it, Naruto mastered wind element and the rasenshuriken in like 3 days, imagine now that the 9-tails is working with him how quickly he can master every other element if he had a few days.
Combine every element into the rasenshuriken where every point is a different element and the center is a spinning tornado of all of them. Think of how cool that would look when it hits and the spinning part expands.
EDIT: He can only throw Rasenshuriken in one of his new modes, SM, KM, or BM because of how dense the center of the rasenshuriken is. They explained that earlier. SM, KM, and BM all increase his strength so that he can throw them and in KM and BM he can even redirect them once they have been thrown and he can make them with one finger.