Xebec the Madara of One Piece verse?
Honestly I hope not? Being Blackbeards father now just makes me think its all meant to eventually hype him and his reveal in a flashback makes me think thats the case since Oda would have probably saved his design for the present otherwise
The only thing I personally see is Rocks actually survived within his son somehow near death, and it explains Blackbeard's multiple fruit/body thing, but thats all Im expecting.
Maybe, like Nika being once a Real person who conceptually turned into a Devil Fruit, Rocks was similar and became a desire so strong that he became his son's first devil fruit? Could be the zoan people are expecting, but the idea is pretty out there lol