They're both going to get the Rinnegan.
Why? The Plot Demands it.
The Sage's ultimate wish was to establish peace across the world, but it was a goal that would never be achieved in a single lifetime. Knowing this, he chose to entrust his strength, dream and legacy to his two sons. The older son, who inherited the Sage's "eyes" (his powerful chakra and spiritual energy), believed that power was the true key to peace. The younger son, who inherited the Sage's "body" (his powerful life force and physical energy), believed that love was the true key to peace. On his deathbed, the Sage chose his younger son to be his successor. Overcome by bitterness and envy, the older son attacked the younger, beginning a war between them. Their feud would continue on through their descendants: the Senju clan and the Uchiha clan.
Naruto? - Sage's Body Reincarnated
- Foreshadow of Naruto's next powerup...
Sasuke? - Sage's Eyes Reincarnated
- Foreshadow of Sasuke's next powerup...
Nagato used Rinne Tensei upon the leaf village to revive everyone who he killed and in the process killed himself. Tobi states that this is a 'betrayal'.
He then says - 'Even if Sasuke becomes as powerful as Nagato (rinnegan), he is no use if we cannot control him'
Ie, even if Sasuke gets the Rinnegan, he's not helpful if hes uncontrollable.
This justifies the theory that Tobi is assuming - Sasuke can get the Rennigan (for what would have been used on Madara i personally believe) - and therefore be able to use the Rinne Tensei. - for Tobi (who wishes to control Sasuke).
Zetsu even states that Tobi 'accommodated for Nagato's death' - by assuming Sasuke would get the Rinnegan eventually - and be used to help him.
He even says that Sasuke can SYNC with GEDO MAZO, the huge statue Tobi is using in the war right now, - which i believe (correct me if i'm wrong) - can only be used by a Rinnegan user.
They will be the end of the feud between Uchiha and Senju.