@artifice, I'm not sure if it's that far fetched, after all, isn't the same thing happening to the 6 Paths of Pain/Tobi ? Ninja with normal eyes, gain special Doujutsu and some jutsu associated with it (Pain's paths), thanks to some chakra imprinting or something. The normal eyes obtain, by special chakra coursing through them, the same or part of the power that the user with the original eyes posses.
One could say, that the normal eyes become a reflection of the eyes that reflect the power ?
The eyes don't simply reflect the power. The eyes are strictly and physiologically speaking, an extension of the optic nerve which is an extension of the brain. The eyes are Neccessary to awaken the power.
Originally Posted by Pure Logic
In Kakashi's and Nagato's case the eyes contain the chakra, and can make more chakra, however the chakra made inside a non-uchiha has been shown to be harzadous and to be a huge strain.
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^ Isn't it more that the eyes convert the user's chakra ? After all if the eyes were producing their own, then they wouldn't have been sucking the chakra out of Kakashi, right ? Seeing as in Kakashi's case, his chakra isn't produced in the proper proportions for the eye, most of it is wasted/scrapped, I think.
This means, that the eyes are in fact a converter for the chakra and the jutsu, while an Uchiha's brain (under certain conditions) release a special mutating chakra, that affect the optic nerves and transform the eyes (it makes normal eyes become the Sharingan and later on become the MS). So just as Hashirama's chakra, filled with overwhelming life energies, can mutate people (especially visible in Danzou's case), a similar thing happens with Uchiha's chakra, that is filled with overwhelming spiritual energies, which mutate the eyes.
This seems also applicable to the EMS, where the new eyes, which are already heavily mutated by the user's special chakra, are then mutated by the new user's special chakra, thus the patter fusing/overlapping. This might also mean that one can achieve EMS, by extracting that special chakra from another Uchiha's brain and injecting it into his own eyes (after the eyes were already mutated to the MS form) ?
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The eyes "being keys" unlock the power? If you have to think about it.... everyone has to be related to the sage in some way. So I could see the eyes unlocking part of the brain causing the people to gain those powers, and if you're an Uchiha once unlocked you can use the powers.... the eyes remind me of the tailed beast and the jinchuurikis. As an example, Gaara still was able to use Sand base jutsus once the one tails, was striped away from him, even though they were weakened a little bit he was still able to do most of his moves. Also the eyes influence growth rates.... like how Kurama affected Naruto's growth "Whiskers, tons of chakra reserves". Once Nagato awaken the Rinnegan "Which requires a massive amount of chakra", affected is overall health, Like how the Sharingan affected Kakashi. Although Kakashi was able to cover it and limit its use. Nagato couldn't and it drain him of chakra and his life forces.