Board Thread:Theories and Speculation/@comment-28939725-20161201164545/@comment-4080775-20161204060131

People are over thinking it. If Nagato could transition his (Madara's) Rinnegan into the EMS or MS, he could automatically meet the requirements for Susanoo. It has nothing to do with Spirit because Kakashi did this exact thing. Kakashi merely took on Obito's Chakra and gained access to both MS abilities and Susanoo simultaneously, despite never using Close Range Kamui nor Susanoo previously.

On another note, anyone and theoretically gain the Sharingan if they obtained the special Chakra produced by Uchiha and channeled it into their eyes, even without Uchiha DNA, because it's literally special Chakra produced in the brain.