Seeing as the Juubi has the Rinnegan and Sharingan and the body powers techniques like TBB and so it would be most likely that the Juubi made the Sage unlock the Rinnegan when the Sage became it's Jinjuriki. The Sage had to be very powerful in sealing techniques to seal the Juubi which is what the Uzumaki are best at. It's so likely that it's had to disagree with...
I would want to believe that, it would explain why the main character is a uzumaki while the story seem to center around uchiha and senju. But how did the sage pass down barrowed powers?
Don't know man, it doesn't explain how the sage managed to passdown his eye and body to his sons if the powers were not his to begin with. Naruto kids will not have Kurama powers, Kakashi kids will not have sharingan, how did the sage pass down a bloodline power that wasn't his bloodline power. It makes no sense