Tobi could have outher path madara and madara himself could summon the gedou mazou and eventually becomming the jinchuuriki of the ten tails!
I wonder why it is so difficult to receive the rinnegan, i mean they have the senju clan = power of the body - sage mode. and the uchiha clan = power of the eyes - sharingan.
Where comes this rinnegan from? i know its from rikudou but its kinda weird it is so hard to achieve while the sharingan and sage mode are much easier.
Or does the rinnegan just has the same story as the sharingan and mneaning its the power of the eyes,, than why is it harder to achieve compared to the power of the body?
Theoretically, the Rinnegan is a manifestation of the Juubi's influence on the body and it happened with the Sage. That's where the Rinnegan came from. The Sage Mode and Sharingan are easier to obtain because they are the highest form of Yin and Yang power-ups (You can include Jinchuriki but for this I won't) and cannot be the Rinnegan. The reason you can't have the Rinnegan without the other half of the bloodline is because the Sharingan will lack the Yang chakra from a Senju to transform the eyes, and the Senju's eyes lack the Yin properties of the Sharingan.
This is why Madara reverse engineered the original bloodlines (The two ancestors who are related to Rikudou) to obtain the Rinnegan.
I would think it would be a forgone conclusion that each son is an extension of the Juubi at this point:
Body (Mokuton)+ Eyes (Sharingan) = Juubi
Hashirama (Mokuton) + Madara (EMS) = Rinnegan (Which is technically reverse engineering the Juubi's ultimate properties - Its sturdy mokuton body and its Sharingan-esque dojutsu).