Hancock is more likely than Caimie. Especially once she gets stripped of her shichibukai title.
I didn't think about it before, but the explanation of Bon Clay's powers seems to strongly suggest he'll be taking the identity of one of the Impel down soldiers. This is actually really awesome because I don't think Bon Clay's ability was properly utilized in the Arabasta arc. I wonder if Oda planned this from the start.