Don't forget about Caribou conveniently being at Egghead where a certain ship is heading. Ancient weapons anyone?
The issue is so many people hated Wano and its ending, that they don't want to imagine Blackbeard invading Wano for Pluton. Because, if Blackbeard does invade Wano for Pluton, we're probably going back to Wano, considering Luffy told Momo that if anyone attacked them, point to the Straw Hat's flag, and tell them the Straw Hats has Wano's back.
If Shiki is going to show up in the Manga, he'll probably be involved with Pluton, too, since he wanted to get an Ancient Weapon alongside Roger, who knew of one.