Board Thread:Naruto Discussions/@comment-36221354-20180717114536/@comment-1872728-20180718142834

1. Hag himself stated that he knew either Indra or his reincarnates will awaken the Rinnegan someday, which is why he left behind the stone tablet for them.

2. The fact that the more you evolve the Sharingan, the more you can read from the tablet makes it seems like the Rinnegan is part of the evolution.

3. Black Zetsu only targeted the Uchiha to awaken the Rinnegan. You could say that it's because they're Indra's descendants and they have the Curse of Hatred, but I doubt there aren't any power hungry Senju/Uzumakis out there.

4. The only people shown on screen to awaken the Rinnegan all had the Sharingan beforehand.

5. Naruto didn't awaken the Rinnegan despite getting half of Hag's chakra.