The Ten Tail's ShaRinnegan also makes me more confident in my notion that the Sage had one set of everything-in-one eyes that eventually got diluted into different eyes among his descendants.
Well, even Kakashi doesn't do that anymore. He did that nail pretty much instantaneously.
I assume it gets faster with practice. But Kakashi will probably go blind before he gets really proficient with it.
Madara's Eternal Mangekyou probably let him train with it till it till he mastered it.
I wonder if the thing where he phases though attacks is the power his other eye has, or if it's the same eye, or if it's an unrelated jutsu.