When do you think he's gonna tell Kaido?
I think he's gonna tell Kaido when he meets him and then hell will break loose lol.
Based on what we've heard from Kaido he's a full-blown, greedy and opportunistic pirate who will get what he wants by any means.
He tried to kill Whitebeard before Marineford but got stopped by Shanks, he is the most likely to have an army of artificial df users so him wanting to have an ancient weapon would make very much sense and he will act once he gets that information.
Also, it all comes together because even though Luffy in latest chapter said he's gonna take on all of them, it's a fact that Law wanted Kaido first for a reason and it will all play out from Big Mam target going from Fishman Island to Luffy to Kaido knowing about the Ancient weapon to Luffy eventually destroying Fishman island to have them live on the surface and carry all Fishmen on Noah.
Oda has this planned out.