I don't think Hancock gonna join, for me she gonna stay an allie for ever. What about Gin Rummy of the Kaido's crew ? It's just little speculation but she has been introduced in Zou's arc without a proper panel like Jack or Sheepshead, maybe she has a low rank among the Beast Pirates but Oda clearly showed 3 characters in the Jack's squad : Jack, Sheepshead and Gin Rummy, why he shows her if she has no importance ? No panel for her and no devil fruit revealed, it's sure she has a SMILE, possibly a snake power different of Marigold and Sandersonia. Also the "G" of Gin Rummy is available in the crew even if you pronounce it "J" like Jinbe. Another thing, Sheespshead (Sheep's head) directly goes to his powers, he has a Sheep Artificial Zoan (and also references the game of the same name). Gin Rummy is a reference to the Gin Rammi, but two others things : "Gin" in Japanese means "Silver". And in "Gin Rummy" you have two alcohols : Gin and Rum. I don't know if it matters but just with her name you can find some things. About her looks, She has pink hair and light blue eyes, + black horns which is quite original in the Women of OP (more than the Hancock looks). But if not her, I will go for an unknown Kunoichi.