Greetings! I'll start right away with my theory! (It's nothing professional,don't get your hopes to high)
As we know probably Kakashi said in early manga that the origins of Sharingan came from Byakyugan.So my theory is that the SO6P was an Byakyugan user,I'm not saying Hyuga only Byakyugan user,Hyuga clan didn't exist back then,so with intense training or some sort of transformation he gained the Sharingan and naturally after fully developed Sharingan comes Rinnegan the Eye's of God.We'll see if this is true if SO6P is showed in some flashback of Kurama again or something else.I don't know about him being an Uzumaki,maybe that is also true,who knows?I'm just a rookie here trying to come up with some theory's.Be polite please.
As we know probably Kakashi said in early manga that the origins of Sharingan came from Byakyugan.So my theory is that the SO6P was an Byakyugan user,I'm not saying Hyuga only Byakyugan user,Hyuga clan didn't exist back then,so with intense training or some sort of transformation he gained the Sharingan and naturally after fully developed Sharingan comes Rinnegan the Eye's of God.We'll see if this is true if SO6P is showed in some flashback of Kurama again or something else.I don't know about him being an Uzumaki,maybe that is also true,who knows?I'm just a rookie here trying to come up with some theory's.Be polite please.