Well I dont know if anyone have already thought on these lines. The following theory is based on couple of discussions i had with my friend. It sounded really interesting to us...
Part 1:
Well we all know one of the Rin'negan's powers; that is to control other body. I was just wondering on it... Lets go back to the incident when Nagato saved Yahiko from the Chunin. Later when Jiraiya confronted him here is their conversation...
Chapter 373 Page 07
Jiraiya: "Whats wrong you can tell me. Is it about what happened earlier?"
Nagato: "When I saw Yahiko get hurt, I got mad..real real mad at that guy... But then I Blacked out... or went out of my mind...When I came back to senses, that guy was grounded."
So could it be that when that Chunin attacked Yahiko, Nagato killed that guy.. but was he contolled by someone!! someone as in the Real Rin'negan User...!!
It could very well be Yahiko is the real Rin'negan guy and he himself used Nagato to kill that Chunin.
Part 2:
Now assuming above theory is true, we came up with another interesting theory...
Its very tempting to see the similarities in the hair style of Yahiko, Minato and Naruto. And am pretty sure its not just a coincidence or that Kishi has run out of faces etc...! This could mean that Minato and Yahiko are related...probably brothers (I havent checked the times in which they lived..someone confirm later)
Which leads us to the fact that Minato is from the Rin'negan family!!!
Now even in Sharingan not all uchihas had it.. It was difficult to awaken the Sharingan.. So rin'negan being even more powerful, it would be even more difficult to awaken it. Hence Minato, even being a genius
couldnt (mistake rectified) awaken it...and sometime later Naruto in some fight out of pure hatred or the will to protect his friends could awaken the Rin'negan..
Knowing Kishi loves his eye techniques, its just too difficult not to think of the main character possessing the most powerful eye technique!! 
Well some of you might not like this theory but still its a vague thought that I came across..Kindly me know of any flaws in this theory
