Board Thread:Theories and Speculation/@comment-4688597-20150531233756/@comment-4912646-20150601023751

The whole eye and body, Uchiha and Senju thing seems really poorly planned out. They're supposed to be equal and opposite like Yin and Yang, but they don't really parallel each other very well at all. From what Obito tells us: We know that under the right circumstances, the Sharingan can evolve back into Hagoromo's eyes, the Rinnegan. This is done by combining the chakra of both his sons to create Hagoromo's own. Meanwhile, it can be inferred that the the Sage's "body" refers to his Six Paths Senjutsu. But to achieve that power, you need to do something that feels sort of unrelated: become the jinchūriki of Hagoromo's mother... which for some reason grants you Hagoromo's power and likeness instead of Kaguya's own. And to make matters worse, you cannot even become the Ten-Tails' jinchūriki without already possessing the Rinnegan, since it is required to summon the Demonic Statue and perform the Coffin Seal.
 * Indra inherited his father's eyes (Sharingan), his genes for powerful chakra, and his spiritual energy.
 * Asura inherited his father's body (???), his powerful life force, and his physical energy.

Logically, it would stand to reason that the lesser eye power (Sharingan) and lesser body power (regular senjutsu) would be equal, but instead the Pain arc treated senjutsu as equal to the Rinnegan itself (at least in the case of transplanted Rinnegan). There's also the issue that only the Uchiha have the lesser "eye" power, whereas anyone could potentially acquire the lesser "body" power, provided they have enough chakra and succeed in the special training.

It gets even worse when you take into account the Rinne Sharingan's existence. It turns out there is an even greater "eye" power than the Rinnegan, but we were never presented with a greater "body" power to rival it. Instead, Kaguya apparently didn't even have any senjutsu abilities, despite being "one with nature". There's also Wood Release, but I have no idea where that fits into any of this, since Hashirama is still the only person confirmed to naturally possess it.