Thing is if the Juubi had the Sharingan traits, and the So6P sealed it inside himself (with just the Rinnegan), how would the Sharingan have been passed down/mutated overtime? Because sealing the Juubi inside himself would not have altered his DNA. This follows that it would be impossible for his sons to inherit any genes which could've later developed into the Sharingan. Unless the Rinnegan and Sharingan are directly related meaning that the Juubi eye is irrelevant in the causation/mutation of the Sharingan.
Madara said he evolved his EMS into Rinnegan, which implies that the two are naturally related. This does then show that the Juubi eye is irrelevant because the Elder Son would've inherited his powers directly from his father and independant of anything the Juubi had.
