Board Thread:Theories and Speculation/@comment-25122992-20170404175224/@comment-4912646-20170405041529

My interpretation is just that it's a specific limitation of Rinne Tensei that a Rinnegan cannot create another Rinnegan. As already mentioned, the remains of Madara's original body should still exist somewhere, so the whole "can't create things that still exist" logic doesn't work for me. Though this raises the interesting question of whether Madara's eyes could have been made real if he'd only activated his Sharingan, unless Rinne Tensei can't make any dōjutsu real.

And about Madara's Edo Tensei being "special", it seems to refer exclusively to Kabuto implanting Hashirama's cells into him, not restoring his youth. Kabuto actually presents Madara surviving into old age as a hypothesis at one point. He says he suspects Madara survived the VotE fight, not that he knows it. Which means for some unexplained reason, Madara was revived in his younger body (and VotE era clothing) without Kabuto specifically intending it. And he was possibly revived without any Hashirama cells either, since Kabuto also thinks his modifications are what created Madara's Rinnegan, and Madara has to correct him.