What I think is, SO6P's younger son inherited the body while the elder son inherited his eyes. He had chosen the younger son, the successor rather than the elder one. Everyone knows the reason why the younger son was chosen to be the successor.
Even the SO6P believed that without full power (i.e, body + eyes) the younger son will restore peace in the ninja world.
And the present story says that Naruto has inherited the Sage's body. But the correct way should be Naruto has inherited the younger son's body. The Bijuus consider him as the reincarnation of the sage because they have witnessed the Sage and his beliefs more clearly which were same explained later by younger son as the weapons to achieve peace i.e. love, and same what Naruto promised the bijuus. That is why the younger son was chosen since he had through which SO6P wanted to create but couldn't because of his age.
But Naruto still consider sasuke as friend and more clearly as a brother, which again goes back to younger and elder son relation.
In order to make Sasuke the reincarnation of the elder son, Kishi will provide Sasuke a new power up i.e. rinnegan. Since the Sage's power was split up in his two sons, who wanted his sons to achieve peace in the ninja world, the reincarnated sons Naruto and Sasuke will either sacrifice together to achieve it or will live separated like the sons of SO6P fighting forever until one survives and achieve his own way towards peace.
This is self explanatory that Naruto will not gain Rinnegan.
