It's a very long theory, but enjoy it. I think that in the past, the Juubi ran rampant, and there was one who was destined to stop him. This man was the Sage of the Six Paths. I think his staff was sent down from the heavens in time of great need to be able to seal some of the powers from the Juubi inside of an individual. Sage of the Six Paths I think was an Uzumaki and was gifted in sealing techs, thus given the ability to do it. He sealed the Juubi's power inside of him thus mutating him and granting him access to what is known as the Rinnegan.
This energy gave him a special and the greatest dojutsu ever to exist, and he used its power to overpower the Juubi and weaken it so that he can easily seal it inside his own body. Thus he became its Jinchuuriki. He had the energy of both Sha and Sen in his DNA.
This is why when he had children he passed on his mutations to his children, Sha Uchiha and Sen Senju, thus making the Uchiha ancestor inheriting the Sha DNA and the Senju ancestor inheriting the Sen DNA. The Sha DNA's dojutsu further mutated eventually into what is known as the Sharingan. Individuals who possess both the Dna of Sha and Sen can get the Rinnegan as it is two energies broken up. This is the primary energy called Rin. This originated from the creator of all things, the Juubi. Rin I think symbolizes destruction and if it is put into the wrong hands it can cause the biggest disasters known in the ninja world. Rin Nohara symbolizes what happened when she died and what it did to someone who loved her dearly. To be able to be with Rin in the dream world he needs the Rinnegan to control the Juubi and eventually become its Jinchuurki to maximize his Rin energy to create a dream world. Obito and Madara only have a small amount of Rin energy. When they have more of it, which is in the Juubi they can do anything the Rinnegan can do, but in a much larger scale. Hope you liked my theory, I tried my best.
Also look at the Juubi's eye.
I think the tomoe are a representation of the Sha energy that are in each of the Tail Beasts the Juubi was separated into. The ripples represent Sen energy. This brings me to my next theory. Naruto WILL GET THE RINNEGAN. Kurama has a great deal of Sha energy in him thus making him so affected by the Mangekyou Sharingan. I think SO6P is a direct
ancestor to Naruto thus making Naruto having his Sen DNA. Neji's death will maximize it due to trauma and stess from his death and together with Kurama he will bring it both together to help him permanently gain access to the Rinnegan. It's long, but I hope you enjoyed.
You must be registered for see images
This is why I think he was waving his staff at him.This energy gave him a special and the greatest dojutsu ever to exist, and he used its power to overpower the Juubi and weaken it so that he can easily seal it inside his own body. Thus he became its Jinchuuriki. He had the energy of both Sha and Sen in his DNA.
You must be registered for see images
This is why when he had children he passed on his mutations to his children, Sha Uchiha and Sen Senju, thus making the Uchiha ancestor inheriting the Sha DNA and the Senju ancestor inheriting the Sen DNA. The Sha DNA's dojutsu further mutated eventually into what is known as the Sharingan. Individuals who possess both the Dna of Sha and Sen can get the Rinnegan as it is two energies broken up. This is the primary energy called Rin. This originated from the creator of all things, the Juubi. Rin I think symbolizes destruction and if it is put into the wrong hands it can cause the biggest disasters known in the ninja world. Rin Nohara symbolizes what happened when she died and what it did to someone who loved her dearly. To be able to be with Rin in the dream world he needs the Rinnegan to control the Juubi and eventually become its Jinchuurki to maximize his Rin energy to create a dream world. Obito and Madara only have a small amount of Rin energy. When they have more of it, which is in the Juubi they can do anything the Rinnegan can do, but in a much larger scale. Hope you liked my theory, I tried my best.
Also look at the Juubi's eye.
You must be registered for see images
I think the tomoe are a representation of the Sha energy that are in each of the Tail Beasts the Juubi was separated into. The ripples represent Sen energy. This brings me to my next theory. Naruto WILL GET THE RINNEGAN. Kurama has a great deal of Sha energy in him thus making him so affected by the Mangekyou Sharingan. I think SO6P is a direct
ancestor to Naruto thus making Naruto having his Sen DNA. Neji's death will maximize it due to trauma and stess from his death and together with Kurama he will bring it both together to help him permanently gain access to the Rinnegan. It's long, but I hope you enjoyed.
I made a complete ass of myself. Sorry ReZ! 
FML seriously, I'll stop using google chrome indefinitely and be more careful. Sorry again.