Ok, we know sharingan CAN copy Taijutsu (Sasuke on Lee)

"[mange] is a physical pupil ability and not a technique/jutsu..." - quoted from raijin

last time i looked it up ... ability~technique.
last time i looked it up ... physical~taijutsu. (~ means roughly equivalent to)

Note now..., Sharingan copies everything - not just taijutsu.

Naruto's Kage Bushin = Ninjutsu.
Zabuza pwnage = Genjutsu.
Rock Lee opening gates inside his body... i don't know what to call that (Uberjutsu?).

Now explain how an external spinning of the pupils can go unnoticed by Kakashi compared to Rock Lee's internal gate opening?

So questions about this "physical pupil ability"
Is this "physical" spinning different from taijutsu?

Even if it is different from Taijutsu - if it can be classified into any normal Gen/Nin/Tai, Kakashi can copy it. And by copy, I mean learn how it is done (not necessarily execute it, as I've stated in my unedited previous post).

If it isn't one of the three normal gen/nin/tai, Kakashi DID copy Lee's "uberjutsu" of the Gates - so what makes Mange special? Both are physical abilities - there is no mystical non-natural explanation.

Edit: About "advanced-bloodline" techniques... although this may be true that Kakashi can't perform the jutsu, he still can copy it - this possibility isn't ruled out by the "bloodline" limitations. Also Kakashi does have blood suitable for Uchiha's eyes, so it wouldn't be farfetched to say that Mange might be accessible by him as well.

This makes sense to me by the fact Kakashi dared to face this technique knowing its effects. He must have had a motive. He isn't stupid.