anyway, ive already made a giant topic on this, but shanks is going to be a very clear villain to most of the crew, and if you remember Sabaody, many of them are already afraid of him. Shanks is the top dog of the Underworld. All the illegal shipping and weapons and drug trade and devil fruit trade goes through him.
I know a lot of people probably look at this and think it's crazy (like even I somewhat "doubt" it), but seriously people need to realize that post Kaido, the whole concept of the Underworld doesn't get erased. The Underworld itself is still an unresolved plot point in this series.
When you combine a lot of those Yakuza motifs Shanks has, it starts to absolutely make sense that he can be behind it all.
Like people don't realize the Underworld EMPERORS were introduced as a concept after Doflamingo lol, so he's never was confirmed to ever run the Underworld. That relevance needs to come back eventually post Wano, otherwise there would have been no reason to introduce it