Well that is his Bijuu form. There's also something about Naruto that stands out from the rest of the Jinchuriki, which the other Jins were talking about, that's why he resembles the Sage of 6 Paths in that form. But it's essentailly the same thing.
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Why would he just randomly decide to give Sasuke half of the Kyuubi's chakra? And why would Sasuke even accept it? Having that chakra is becoming an everyday thing now, I swear lol. It's not unique at all anymore.
"If you will not listen to reason, then listen to my fists!" "You were always a brother... Never an enemy."
You know how Orochimarus arms "souls" got put back into his arms without him seemingly doing anything? Maybe the sealed half of Kurama is on its way now to go merge with Kurama(i.e. Naruto) and then hell have a complete form.