naruto still has another upgrade coming.
It'll happen one of two ways, maybe both.
At one point i think both kurama's will need to merge.
My theory then after is that since naruto is able to share his/kurama's chakra with everyone, then in theory everyone should be able to share their chakra with naruto.
Everyone is linked already so i don't see this as too far fetch.
Soon as one or both of these things happen, naruto's current eye combo mode with change again and he'll achieve rinn eye's.
Either that or someone's going to give naruto an uchiha eye or dna. Doubtful though.
I see it going the other way, the rinn eye's have to be created naturally, which would explain where the sage of the six paths achieved his form.
It will also culminate what the entire series has pushed, that being naruto being "the chosen one." Chosen by birth and by the people when they transfer their chakra to him.