The Rikudo Sage has returned, and he bears a Sharingan!
Look at the following picture and ask yourself this question: Which one of these things do not belong?
The answer is: none of them. They are the same. Sasuke is the Rikudou Sage. Yes. The Rikudo Sage has been reborn in Sasuke Uchiha. Want more damning evidence?
How can anyone ignore that? Have we ever seen something that crazy for anyone else? Look at the hair, eyes, and neckband. Just like the Rikudou Sage, Sasuke Uchiha will also bring peace to the ninja world with the Mangekyo Sharingan, which will go down in history as the most powerful dojutsu in history since the Sharingan. The Rinnegan is the so-called most powerful eye and a tool of heaven blah blah. However, Sasuke Uchiha is the man with the "power in his eyes". Why didn't they call Nagato the man with the "power in his eyes" if his eyes have such power? Cause they don't.
The Mangekyo Sharingan has the power!
All of it's jutsu have something to do with legendary gods! Continuing on, Sasuke will bring peace to the shinobi world and is willing to be a sacrifice. In fact, look what he tells Naruto:
Even Suigetsu knows it:
Sasuke is the Rikudou Sage.
This is a dummy theory that walks between probable and possible, like Obito=Madara. Some will take it seriously, and others won't; It's not meant to be debated.