I really want him to get the Elder Son's Dojutsu+Perfect Stabilized Susanoo (With the obvious benefits of his amazing Amaterasu proficieny). I don't think Rinnegan suits him, because it doesn't really fight like the other two Dojutsu's. It's more of a large scale chakra taxing technique, which I believe suits Naruto who needs it to widen his limited arsenal.
It'll be like this:
A clash of the Sage's ideals and powers (Naruto) vs The Elder Son's ideals (Sasuke) with the powers of each being similar to predecessor they are related to.