Well with that logic he could have a full blown 10-tails inside him. Given that Obito/Madara had a piece of Hachibi/Kyuubi chakra yet managed to resurrect the 10-tails there is no reason why Naruto shouldn't either. The only thing missing is the body, but then Naruto could absorb the chakra in himself or just have it exist like the Kyuubi does inside him now.
Amaterasu would be very useful right now against the 10-tails. Just create the flames on it's eye and it will keep burning making the thing go wild.