Opening that left eye is not necessarily something related to a mastodonic power up I guess. It could even merely be a way for Oda to portray another parallel with Rayleigh and pretend that his eye for some reason was healthy again and it was never permanently damaged that extensively.
Fights with 6 swords, is themed around a blue dragon (Oh hi Kaido), is a loveable and strong badass and has the same voice actor as Zoro, at least the Sengoku Basara version of him but maybe the Samurai Warriors one too?
Zoro's VA also voices this legendary badass, who once
pulled out his own eye after it was shot by an arrow and ate it!
And then finally, we have the legendary Zoroki Kenpachi himself! If you know about Zaraki Kenpachi, enough said ofc! Badass, extremely strong swordsman who loves to fight, gets lost frequently and easily, is a complete powerhouse and beacon of hope for others with his own adorable, pseudo daughter, pink haired, little girl companion too!
After Rooftop Piece though, I've given up on Zoro opening his eye almost entirely. My last hope is his final fight with Mihawk where Oda will hopefully elaborate on it on-screen (and not in a vivre card/SBS/databook/light novel etc sigh) and show how and why Zoro lost it.