The first clue leads us to the fact that during Itachi and Sasuke's fight one of the techniques that Sasuke Uchiha could not counter was Itachi's last move, Susanoo. That being said, it is climatically logical for this particular technique be the one Itachi Uchiha has relayed unto Naruto. The huge cloud of smoke dispersed about Naruto after the technique ties in with the humongous size of the summoned creature when Susanoo is performed.
There could be plenty of theories and speculations, but this is what I have hypothesized to be the answer to this mystery without depending on the manga. It will be eventually revealed as the story progresses. However, it would seem that Naruto would be attempting to somewhat synergize his three most powerful arsenals; the demon fox chakra, sage mode and sosanoo. I am certain that it will be one amazing revelation when it is eventually animated.
