I have a crazy theory and it's that shanks would be a straw hats or he's playing an extremely big role at the moment and the reason is that ,you know before every start of manga there's an overview of the current story and CHARACTER IN THAT ARC. I've noticed this since the starting of manga that no matter what arc ,even if there's no shanks he's under the straw hats banner which is surprising and to top it off currently in wano ,I see a section of beast pirates,akazaya nine etc and straw hats and under them it's SHANKS. This is not much to conclude this but considering oda sensei is highly likely outcome. GIVE ME CREDIT IT THIS COMES TRUE.