No one will ever be the next true Sage of 6, only one close enough is Naruto since he now possess Chakra from all 9 beasts, Sage mode, and he established a relationship with all the tailed beasts.
But then there is the one piece of the SO6P piece Naruto is missing the Ocular powers; the eyes of the Sage now if Sasuke gives his eyes to Naruto or if Naruto obtains Madara's Rinn, then Naruto would possess all the pieces to be the next SO6P but I don't think either one is going to happen and Naruto is going to be Naruto and Sasuke might realize he truly loves Naruto and see's him as the closest thing he ever had as a real brother (like he did when he left the village)
But then there is the one piece of the SO6P piece Naruto is missing the Ocular powers; the eyes of the Sage now if Sasuke gives his eyes to Naruto or if Naruto obtains Madara's Rinn, then Naruto would possess all the pieces to be the next SO6P but I don't think either one is going to happen and Naruto is going to be Naruto and Sasuke might realize he truly loves Naruto and see's him as the closest thing he ever had as a real brother (like he did when he left the village)