The reveal of who Kaido’s son is, whether it’s a character we know or not, will be an exciting moment. If it’s a character we know, it has to be a big important character or one we’d never expect.
There’s the theory we already saw his silhouette back in Punk Hazard. When Luffy beats Caesar, there’s someone we see saying “Call Jack”. He looks like someone from the Beast pirates but his silhouette doesn’t match King, Queen or Kaido.