User blog comment:Kaido King of the Beasts/Chapter 906: What is This, a Crossover Episode?/@comment-24850639-20180601152149/@comment-244290-20180604024306

"Just because Doflamingo happened to be talking about it before those panels doesn't mean that it's automatically going to be the next thing Oda shows."

It very likely does.

Not enough to confirm it... but come on. That hat has as least something to do with the national treasure.

Maybe Roger stole it and left a calling card.