This is why I don't think the sage is an uzumaki
That form you're talking about is the ninjutsu he invented for the juubi that creates a jinchuuriki and passed down
You must be registered for see links
That means he already had that form that naruto uses this one
You must be registered for see links
The sages body that the younger son inherited had the body,life-force,and yang chakra
You must be registered for see links
Narutos cloak was filled of life-force
You must be registered for see links
The guy in the juubis mouth symbolizes the sages body (younger son)you can see the tomoe necklace the swirls,staff,and scroll on his back
I think those swirls are supposed to represent life-force and yang chakra
You must be registered for see links
It takes naruto an uzumaki all of kuramas yang chakra to resemble the form that the sage looked like when he used the seal
The younger son inherited boy life-force and yang chakra and he probably could have that form too if he knew the seal
But the younger sons blood thinned and his descendants were loosing that chakra that is until an uzumaki gets all of the strongest bijuus yang chakra to make up for that