I liked the theory but you made a mistake that unties the scroll to the Sage. That thing behind his back is not a scroll it's his arms. Notice how there are hands sticking out from both ends, and how on the left side the hand is holding the staff. So no, it's not the scroll.
On the other hand the So6P was the very first Host, and we admit that all other hosts became so with a technique based on Rikudo's. That the scroll would have been seen by many people and originated all the different ways of sealing a beast. That is unrealistic.
I'm not saying I don't agree with you, the Sage being an Uzumaki is quite plausible at this stage, but the arguments you brought aren't strong enough to provo or give this theory any special edge over any other.