Oh, yeah. That's definitely looking like a Wano hat shape. Now I am sold on the Person with crocus on the cover. Still 50/50 between shiki and gaban. In Chapter Zero, Shiki accuses Roger of knowing the location of an ancient weapon, we also see Gaban in this panel. So Roger knew about the ancient weapons way before, and he could have entrusted the location to his crew mates before he got executed.
On the other hand, we saw Shiki in a wano flashback, so he too could have gotten that hat from there. As to why he would have sat down with Crocus all friendly, like exchanging drinks together, but then again, even enemies respected each other and often came together like that despite their differences. Shiki also respected Roger. Oda could definitely introduce shiki back into the main story now that the ancient weapons are exposed to the world.
This mysterious Person acting all friendly with Marco being Shiki wouldn't be too farfetched either, given how Shiki casually visited Prime Beards ship and talked to him. And as former crew mates during Rocks Era I bet Kaidou didn't mind him either.
Shiki says here "The Wall that stood before us has disappeared" as in, the wall in Wano kuni is now ours to breach to get the Pluton. Okay, I see myself out. Enough nonsense for today.