I know that it will take some time to learn sage mode. and the rinnegan theory is plausible however, i am not sure its on how to activate the rinnegan. So far from what we the reader know is that Madara is the only one who knows how to activate it and Orochimaru and Kabuto had a theory to unlock it. Meaning they cant know if there theory is correct since they have no one to try it with(ie sasuke) and they dont know if it will work. So the rinnegan activation is highly unlikely. Its like saying "Oh i know how to to control and compress dark matter for an unlimited amount of energy". The only way it can be confirmed how to unlock would be for Madara to explain it. I like Blaze Release forum(cant find btw) how he believes the rinnegan was unlocked by Madara losing to Hashirama. If that is true, then Sasuke needs to lose to Naruto or Someone stronger than him. Who knows maybe sasuke will pull a madara and come back after unlocking rinnegan and then looking for the Dragon Lair. Again this is all just speculation