According to Madara Uchiha the way he obtained the Rinnengan is by implanting himself with Senju DNA while having EMS. Also he said that it took him nearly to the end of his life span in order to unlock the Rinnengan.
Theory: Rinnengan Delay
I think that the reason it so long for Madara to develop the Rinnengan is because it took that long for his yin and yang to balance. Madara's spiritual chakra is the highest among the Uchiha therefore it makes a lot of sense that if possible it would take the raw harvested cells years and years of growth until it reached the level in which its yang could balance out his yin.
What makes Hashirama's cells so special is that they are self replicating cells that produce strong yang chakra and as the cells grow they strength the users body and even allow the user to utilize their own chakra in order to perform wood release. The Yang chakra that Naruto produced from his Chakra cloak was shown to be so strong that it causes Yamato's wood release to grow into trees. This fact along with the fact receiving kyuubi chakra from Naruto was enough to permanently enhance Kakashi's Kamui to the point that it almost rival's Obito's and seemingly erase the physical damage brought upon by using MS techniques could prove that The Kyuubi's yang chakra produces an affect very similar to senju DNA.
If this is true then it could be that all Sasuke would need is enough Kyuubi yang chakra to balance his own yin chakra and therefore allow his to activate the Rinnengan.