He literally acknowledged him more than Luffy by saying that if Zoro joined him they would take over the world.
If you think about it, Zoro calling himself "King of Hell" could foreshadow this very thing happening, but instead Kaidou would be joining Zoro to take over the world... Oda is definitely leaving what "King of Hell" really means open to interpretation for a reason.
There are plenty of places Oda has named "Hell", but what does a "King" need as well? A Queen. I think Zoro's path to becoming "King of Hell" is through the "Princesses of Hell". These princes or princesses of hell could be Perona from Thriller Bark, Hiyori of Wano or maybe Yamato from Kaidou's reign as King of Wano.
There are some other candidates as well. There are no princesses in Impel Down, but if we want to do some reaching, you could say Magellan is king, therefore since his ability is poison the only poison princess we know is Sanji's sister Reiju.
I also think Lilith is Vegapunk and Stussy's daughter. Since Stussy is the empress of the "Underworld", this would technically make Lilith a princess of hell as well. Drug Peclo wields a scythe and wears the chapter number 499 redirecting you to Zoro nearly killing the Chalros the Celestial Dragon. There are also a couple supernova there to comment on this event, and I think Bege's involvement in the Underworld and Apoo's affiliation with Kaidou, Wano and the Numbers foreshadows them possibly joining Zoro in the future as well.
Assuming Lilith should have connection to egghead's database and Vegapunk's memories, then when Franky mentioned Vegapunk's lab Lilith remained silent. Lilith's name also has a special meaning when it comes to Zoro's connection to King of Hell.
I think the dualism with Luffy's brothers and wings is pretty obvious. Sabo and Ace both used the power of the fire fruit, and both Zoro and Sanji drew power from science and lineage factors.
Zoro's lineage factor most likely involves Kaidou since both he and King are shown as two prominent test subjects. Since Zoro in this dualism is Ace the son of Gol D. Roger I think his lineage factors are special as well. Right now my list of lineage factors Zoro has is connected to his Nine sword Asura form, and I think the name Nine red scabbards could hint that the 9 swords are actually Zoro's lineage factors peeking out.
I think Shimotsuki Kozaburo was a scientist as well, and Enma was a science sword that ate a copy of Smoothie's fruit. This means Kozaburo not only was around when Vegapunk achieved artificial fruits, he was also involved with the science of feeding fruits to inanimate objects.
I think Vegapunk used Sword God Ryuma's body as a base and created a monster like artificial devil fruit related to spirits. Vegapunk and Kozaburo then fed these spirits multiple artificial devil fruits. I think they fed Zoro's spirits Kuma's fruit, Whitebeard's fruit, and Kaidou's fruit. Right now I think Zoro's possible lineage factors are Kaidou, Whitebeard, Roger, Xebec, Shanks, Mihawk, King, Ryuma, Oden, Dragon and Kuma. There are multiple instances where Zoro is indirectly painted as a brother to one of these lineage's children. Right now I'm 100 percent certain Ryuma, Whitebeard and Kaidou are locks. Based on these brotherly hints I think Roger, Oden, Dragon and Kuma are being hinted heavily at. Xebec, Shanks, Mihawk and King are toss ups for me.
My theory is Zoro as King of Hell is going to absorb all these factions into one, and use Wano/Pluton as a fortress. King of Hell and Sword God are two different things, just like the right hand of the Pirate King and World's strongest swordsman are. Just right there are FOUR different titles. We might as well include Monster samurai, World's strongest man and world's strongest creature as well. Hell, Zoro will even become king of the world like Xebec wanted to. You could even call Zoro Green Hair, which Sanji practically already does. Just right here are NINE incredibly important titles connected to Zoro. Soro is endgame.