Theory on Kaido’s connection to Wano and potentially what it means for the story:
In chapter 970 Kaido expresses knowledge on “The old Kozuki”, Kaido arrived in Wano only after Orochi became Shogun, With Sukiyaki being dead for some time. It’s unlikely Kaido would speak of the Kozuki with such familiarity if he was an outsider.
I’m suggesting Kaido was once a resident of Wano long ago, we’re already aware of two outlaws in the past who fled Wano, those being Shimotsuki Kozaburo and Kurozumi Higurashi. And I think I may have an idea off which clan Kaido belonged to.
The top of this page seems initially quite random; showing The Flower Capital and Ringo alongside each other, neither sharing a connection to the current events. Yet if you pair the top and bottom half off the page it creates a link; Kaido – Ringo & Oden – Flower Capital.
Kaido only recently built his Mansion on Onigashima 20 years ago, but where did he stay for the 6+ years he occupied Wano? We know it’s not the Flower Capital. Based off the battle with Moriah it seems he stayed in Ringo, a winter country and moved to Onigashima a winter island.
Kaido seems to have a connection to Ringo, the region of Wano ruled by the Shimotsuki Clan. What I’m theorising is that Kaido could in fact be a Shimotsuki, he could have left the country alongside Kozaburo. And he could hold a connection to Zoro’s lineage.
*Theory by Kinky Grape