You are making this look like its not a theory anymore but a prediction of what will happen. Look the Uzumaki's have been the 9 tails jins just because they have a strong life force to hold back the nine tails. You dont realize the difference of the seals used to seal nine tails in these three jins which are Mito, Kushina and Naruto. Let me tell you the difference.... in Mito and Kushina's case their seals were designed to hold the kyuubi at bay and not do any harm to the world and free from shaingan users.
But in Naruto's case the seal used was a seal that allowed naruo and Kyuubi to co-exist with each other and read each other's emotions. Now I am guessing that Mito and Kushina both used the same seal that like imprisoned the Kyuubi inside themselves and it immobile to do anything.
Oh and about SO6P seal... what are you talking about?
About the SO6P Seal: Kurama actually RECOGNISED the Seal itself as the Sage of the Six Paths own Seal when Naruto used it on him after extracting the Kyuubi Chakra. He looked shocked and surprised that Naruto could use the SO6P Seal. Read the Manga again.
Obviously Uzumakis are best hosts because of their Chakra reserves, however regardless of that: If Mito and Kushina did NOT use the SO6P Seal (evidently they did not my bad, Naruto only used that particular Seal after defeating the Kyuubi with the help of Kushina) it would only stand to reason the NARUTO could use it because somehow there is a connection between himself, the Sage, and Kurama! Are you not seeing my point?
That and the fact that all of the other Bijuus also recognised a familiarity with The Sage of the Six Paths when they all gave their names AND chakra essence to Naruto.
In regards to the Seal itself POSSIBLY holding some of the Sages Chakra: I am referring to the Sages Consciousness. It would make sense as the Seal itself was used by the Sage and also connected and controlled the Yang Chakra flow between Naruto and Kurama.
Still, even if thats not the case, i still think we are going to find out more about the Naruto/Sage/Kurama/SO6P Seal Connection.
Totally agree with Sir Derp Obitos post. Also think the Seal is relevant. As well as the 'Consciousness' of the Sage and his Manifestation. The other half of Kuramas Chakra included.
And for the record: It's just a theory. NOT a prediction. I have yet to hear your theories on things. All you have said is you disagree you disagree.