So, I have a Theory about Kaido and his DF if he got one
I think of a Koi Zoan.
A Fish Zoan is totaly what Oda would do. A totaly useless DF at first glance, but mastered to a perfect extend.
Aso, there is the chinese Koi Legend, in wich the Koi can become a Dragon.
And Dragons are said to be the most powerfull creatures.
>Kaido has Whiskers, like Koi Fish and chinese Dragons
>His Lore so far and his appearance implied Asian History (connections to Wano, again his Whsikers, shimenawa ropes around his belt)
>Koi Fish tend to be said to bring luck, and Kaido is very lucky (escaping captures, breaking blades, etc)
>DF Abilities are not canceled by Seawater (Luffy is still able to get streched)
>so he would be able to breath under water, thus can't drown himself
>His drop from the Sky sland could be a nice reference to a Magikarp Splash
>like a Magikarp Splash it did no damage, at least to himself, so it didn't do the intented thing