If Naruto is going to inherit Hiraishin, it'll be in The Last. I was looking foward to him using it as a solution to gathering natural energy, and countering
Tobi's Jikūkan Idō.
Kishimoto's probably going to be a dick and just give it to Kakashi to make up for his loss of the Sharingan. Tch.
Ugh, everybody's been suspected of being Jashin, or related to it somehow since the Immortals arc.
Because there isn't actually a silhouette there, which is even more apparent in the Viz and tankobon releases. It's just part of the rocks.
I sincerely doubt Naruto would have failed to notice somebody watching from that distance. And if Kishimoto wanted to allude to somebody observing the battle, he would've left a more prominent clue; like Hashirama's reaction to what turned out to be Black Zetsu after defeating Madara.
Doubt he has enough chakra for Rasenshuriken.
Rocks would've been okay though.