To clear up some stupid thing I have read.
Madara- The rinnegan is the final formation of the sharnigan, Madara claims to have awakened it not long before his death, he said to obito that he gave his eyes away, most likely to nagato, probably knocked him out and implanted them which is why nagato didn't remember anything. Who madara got his one eye is really a mistery because the Uchiha Massacre has not happened yet. so he must have obtained it from an Uchiha that we know little about. Old Man madara will probably die soon, after he corrupts Obito to follow through with his plans. I suspect he uses Rin to finally make him corrupted.
Obito and Kakashi- When they were both kids they had the reverse situation as Saskue and Naruto. Obito childish was always trying to catch up to Kakashi, and it seemed like Kakashi was going the wrong way in life. After obito's death kakashi changed for the better. Now we are in the future and now Kakashi and Naruto both have a best friend who is a vengful Uchiha.
I feel that Kishi will somehow tie all that in together.
Nagato- He was a perfect choice for lending the Rinnegan to because as an Uzumaki he has a strong life force, and naturally a lot of chakra, he was planning the whole time be rived by Nagato because he has the chakra nessecary to pull of such a powerful jutsu