That's not how it works. Rinnegan requires Ashura and Indra's chakra to be mixed, producing Hagoromo's chakra. The Rinnegan is also still the final result of the Sharingan's evolutionary line. Naruto doesn't have Sharingan, so he can't magically sprout a Rinnegan.
Hagoromo was worried about Indra or his reincarnations awakening the Rinnegan, since they were the ones with the Sharingan.
But Kakashi sprung a Sharingan after Obito's eye was taken, so why can't Naruto do it?
So say Naruto kills Sasuke and takes his moon seal.
Then he will develop the Rinnegan.
He can make his rasengan take on bijuu characteristics.
So here, he can make a Rinnegan Rasengan.
Perhaps the Rasengan would look like a Rinnegan eye but will ultilze all Rinnegan abilities upon impact.
The rasengan will look something like this
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So say Naruto kills Sasuke and takes his moon seal.
Then he will develop the Rinnegan.
He can make his rasengan take on bijuu characteristics.
So here, he can make a Rinnegan Rasengan.
Perhaps the Rasengan would look like a Rinnegan eye but will ultilze all Rinnegan abilities upon impact.
The rasengan will look something like this
You must be registered for see images