What if Shanks didn’t intercept Kaido to stop him going after Whitebeard? What if Kaido was the one who delayed Shanks’ arrival in Marineford?
We know Shanks and Blackbeard share a hidden bond, which makes Shanks extremely cautious about him. No one could have foreseen what happened after the duel at Banaro Island. But Whitebeard himself had an uneasy feeling regarding Ace’s hunt and Shanks personally came to Whitebeard to make his request. Out of the million scenarios, Shanks predicted the most dangerous one and tried to stop it.
So what if Shanks somehow knew Blackbeard would show up at Marineford to make his play? But due to Kaido, he was delayed. And in those moments, Blackbeard unleashed chaos on Impel Down, gained a mighty crew and stole one of the strongest devil fruits in the World. By the time he arrived, Blackbeard had already become a massive power.
Which makes me think the Reverie will lead to another such moment. Shanks warned the Gorosei about Teach.
But as soon as the Reverie ended, Marines went after the Shichibukai and we see Blackbeard getting ready to make his next move.
*Theory by pice0fshit