Board Thread:Theories and Speculation/@comment-29769110-20161017201027/@comment-30323490-20170912134237

Rinnegan can be awaken if you posses both Asura and Indra's chakra/cells from both reicarnations/Hagoromo's chakra. Theoretically speaking, everybody can awaken the rinnegan if they somehow reproduce Hagormo's chakra. Even Shikamaru for instance could awaken the rinnegan if he would posses parts of Naruto and Sasuke, or Madara and Hashirama, or any combination between the 2 types of reicarnations. Having the sharingan is not a requirement. The fact that only sharingan users awakened the rinnegan (except Hagoromo) is not necessary a coincidence, i wouldn't call it that. It's more symbolic, since both Madara and Sasuke are symbols of dojutsu, and share this common trait from Indra. But having the sharingan is NOT requirement.Technically, Madara lost the sharingan power in his left eye(i think left) after he used Izanagi to escape death against Hashirama, yet he still awakened the rinnegan later in that eye.