I am going to say only one thing. Or maybe two. 1) Rules in Naruto are clearly meant to be broken. 2)Twists sell.
We know mixing Senju + Uchiha creates the Rinnegan, we also know the Uzumaki can also show the S06 powers as evidenced by Nagato (the rinnegan - Tobi couldn't have given Nagato the actual eyes because Madara didn't have them yet), Kushina (Host of most powerful Bjuu), Mito (same) and Naruto (S06 cloak). You could wave that off and say it is because they are part Senju, but none of them are related to the Uchiha. So there is wiggle room.
First off, the "rules are made to be broken" and the debate about history happens because Kishi rectons the manga and changes his own story.
We recently (in terms of the storyline) found out the Uzumakis were an off-shoot of the Senju clan. And it wasn't stated as a rumor, it was stated as a fact, as in the Uzumakis haven't been around long enough for their origin to be in question.
Secondly, anyone can use the Rinnegan once it's already been activated. We've seen non Uchiha's use the Sharigan, and non-Hyuuga use a Byuakygan.
Madara gave his eyes to Nagato, we know this. Does it necessarily make sense yet? No, but Madara has stated he gave Nagato his Rinnegan eyes so it's a fact, not up for debate.
Not one Uzumaki aside from Nagato (thanks to the Rinnegan) has used the powers of the Sage, so I'm not sure where you are getting that idea. Hosting a Biju is not a power of the Sage, nor is Naruto activated the Sage's cloak via his fathers seal with the Kyuubi's chakra.
remember this guys...
My theory is the Uzumaki branched from one of the earliest Senju generations, it very well could be the Younger son had 2 kids, one of them continued the Senju line and the other gave rise to the Uzumaki clan.
They are specialized sealing experts with special chakra and long lives, they describe what a Senju is better than the actual Senju do. Their clan was probably kept very pure compared to the Senju who diluted into Hashirama and then into nothing noteworthy.
That pretty much is the only way to make sense of the Uzumaki and Naruto's connection to Rikudo.
And there is a reason to doubt he is an Uzumaki. His sons were the for fathers of the Senju and Uchiha clan. The Uzumaki's were descendants of the Senju. How in the hell could the Sage be from a clan that didn't even come into existence until long after his death?
The whole reason Naruto is able to resemble the Sage is because he is an Uzumaki, a clan the descended from the Senju and share a lot in common in them. He also has a seal on him that is based on the Sage's designs, and he has the Kyuubi in him, which is giving him amazing life force and new powers when it's chakra goes through the seal.
I really don't understand how this is even up for debate.
it could also be the mother of the 2 sons (SO6P had a wife?)...later gave birth (maybe with someone else...maybe being pregnant when SO6P died)
Or he could have had a brother/sister who had children
Or he could have had more than 2 sons
Or he could have had a daughter
Or he was revived
So many possible ways for his blood to start a third lineage
do put some consideration in it..
so6p had two sons- one got the body and the other got the eyes
has ever been stated that one son=senju and the other uchiha???
i find it interesting the uzumaki are more closer to so6p than senju...
they have longer lives and sealing techs..which were needed to seal the jyubi...
it is even shown that uzumaki can survive the extraction of biju.....
Just food for thought.....
If u read kushina's convo with naruto she specifically stated that uzumaki were known for 2 things: sealing techs and long lives....
So6p is still a mystery..i base my theory on the fact that i believe jyubi is the origin of all ninjutsu..before so6p there were only sealing techs...and uzumaki's were expert in it
the so6p needed those techs in order to seal the jyubi inside of him....