Now i just though of something.
In the newest chapter, we just learned that the Uchiha inherited the eyes of the sage of the six path. Now we all know what the sage of the six path had the rinnengan and the uchiha had the sharingan.
But I believe sasuke is more than a regular uchiha, he is the Destined avenger of the Uchiha clan. Like he said, his dreams are not of the future but of the past, where he lived amongs the uchiha clan...
For the eyes, we know they can be implanted, like kakashi and danzou, or even in mandara case, he implanted his brother eyes to get a Eternal Mangekyo sharingan.
Now what can be Sasuke powerup? He has the sharingan, he has the mangekyo sharingan, but what IF, within his sharingan, he awakes the rinnengan? Woudn't that be plosible? Pein has awakened his rinnengan though suffering and hate. Sasuke has enough hate in my mind to awaked these eyes, on top of his sharingan.
Let me know what u guys think!