Maybe, it would be better to start considering the possibility that Naruto obtain the Rinnegan. DO you noticed that chapter 630 confirmed that Naruto has the other tailed beasts inside him? check here for this confirmation from Edo Madara.
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If you can read properly, Madara stated that Juubi is panicking because he probably saw the Biju
s inside Naruto. First, I will say that Madara is confirming that what Juubi reflected in chapter 629 is actually what he saw, and it also mean that Madara can see the same thing inside Naruto.
Second, what Madara does not know is that Juubi also saw Naruto developing the Rinnegan.
The truth here is that Juubi is not the only one going through transformation. At each new transformation of Juubi, it has been shown that Naruto also get a new transformation (or power up). Thus while Naruto and Co can see Juubi transforming, Juubi also see Naruto transforming. This look like a duality in the two power.
Whenever a Juubi arises, a Rikudo will arise as well to stop him.