Sasuke would need to have Senju DNA like Madara and Obito have to gain the use of the Rinnegan like they have Senju/Uchiha DNA is what lets Madara and Obito control the Rinnegan. As for Naruto who is a Uzumaki His DNA is complete but I can only see Him have the Rinnegan if He takes the Juubi power into Himself like the SO6P did long ago,that maybe what Kishi dose in the end all the tail beast and their powers in Naruto's body giving Him the Rinnegan and power over Madara and Obito. Maybe the next chapter 616 will be the beginning of that.