im hoping that itachi will reveal more about his gift to naruto in the next chapter, i personally think its going to be similar to madaras "gift" to nagato ,meaning that his rinnegan was a mutation caused by the introduction of uchiha dna into a decendent of the sage who has inherited the younger brothers life force and thus possesses enough chakra to fuel it (which means that naruto also possesses this hidden ability). i feel like this is where kishi is going with this but i highly doubt that he will introduce this ability until after his battle with sasuke ,to keep things even,( possably as a direct result of madaras "liquidation" of sasuke in the event of his defeat); just a thought