This is just a quick theory/analysis I have, so feel free to improve upon it.

Out of all the eye Dojutsu, the sharingan is the only that mutates multiple times.

The sharingan first starts with 1/2 tomoe, then 3, then you must need to go through a tragic moment in life to awaken the MS, followed by replacing your eyes for EMS, and finally evolve to rinnegan with Senju DNA.

The sharingan also grants new abilities with each stage, and it did say that the EMS grants a completely new tech(meaning not Perfect Susanoo because that's only a variation, and not rinnegan because that requires senju DNA)

it's quoted as a "new special technique"

Each user's sharingan are granted both both different properties(kamui, KA) and some common ones(susanoo, amaterasu) and also each Mangekyo Sharingan looks vastly different between users.

but both the byakugan and rinnegan have no stages such as the sharingan, they both give the same common abilities as far as we know, and they all look the same.

Also both the byakugan and rinnegan can't cast genjutsu while the sharingan can.

We see both Oro and Kabuto try to go after the Uchiha(sasuke/itachi), rather than go after Nagato(who possessed the rinnegan) to uncover the true knowledge of ninjutsu. They didn't know that Madara gave away his rinnegan, and for them to believe that the sharingan was more important than the rinnegan, must mean there are still thing to be revealed.

The sharingan almost has no similarity to Byakugan and Rinnegan, yet it's the only one to be able to evolve into the rinnegan.

and if it is a simple mutation, how would senju DNA grant evolution? Would giving Uchiha DNA to a senju grant him a sharingan or rinnegan? It doesn't seem like that would be the case.

Does this also mean that there are still secrets to the rinnegan and byakugan(having stages uncovered yet)?

Opinions, thoughts?