Do u think he would loose Shusui?
Since it was his go-to sword, I feel it becomes pointless if he return it back.
As he didn't stole it rather earned it from Ryumma himself.
Also it gives him a purpose to cut Kaido as he needs to prove to citizen of Wano that he rightfully deserves Shusui.
I don't know if Oda will increase a lvl of his sword. I mean Enma was wit Oden n that sword didnt become black neither was Wadi Ichimonji who was in the family of Kuina. Both the swords were from Wano n prolly used by some big Samurais.
And Zoro definitely don't want to lvl up Sandai kitetsu - The cursed one as it brings terrible death to its owner. It might overpower his luck.
He already lost Shusui and was given Enma in return. It would have been rather pointless to give Zoro Enma, to let him master it, use it in their fight against Kaidou, to in the end have him return it and be given back Shusui. The fact that there were no issues for him to wield Enma, Oden's sword of all people, but everyone flipped out about Shusui, speaks volumes.
And as I said why would Oda introduce this concept now of all times? But then not use it?
The explanation of this concept and the process behind it are still vague. However, most likely the higher the rank of a sword is, the higher the threshold is to raise it even more. Shusui is already a 'Black Blade', raised by Ryuuma. As Shuusui is part of the 21 Great Grade Swords, it probably was of a lower rank before Ryuuma. There's currently only one rank above that (12 Supreme Grade Swords). So for Wado Ichimonji & Enma, which already have the rank of Great Grade Sword, it's far more difficult to raise it and it requires a swordsman of an extraordinary caliber.
Currently, there's only one existing character that comes to mind that could/has pulled this off: Mihawk.
Zoro is the character whose reaction on a sword that drains its wielder spirit in an instant was 'I like it'. So, I'm pretty sure he has no reservations about potentially raising Sandai Kitetsu.
