he can, as he already could with Shusui back in TB.
The reason for Zoro not having a black blade is his lack of strength.
Yoru > Zoro's swords because Mihawk > Zoro
I dont think he can. Not the real benefits that are still unknown to us readers.
I dont think a heavier and/or harder blade is all there is to it.
For such a rare achievement it has to be something pretty fking amazing.
Zoro doesnt lack strength, he achieved a bigger feat than Kaido's top 5 - a scar with CoA alone.
He is powerful enough to take out 99% of the universe already.
However, it just so happens that all his future opponents have a form of invincibility and all the power is useless.
The exact concoction that makes up a Black Blade is not known yet.
When we get to that part we will see what he was missing.