I think WCI was the last chance for Gin to come back in a meaningful capacity. He revolves around Sanji, so he will come back at a time when Sanji is focused on. That isn't Wano. Sanji's role here is as a fighter, there are others who are getting a character focus.
Now, all I can realily for Gin is an epilogue, Sanji's got the Baratie in All Blue, feeding everyone, and Gin comes through the door for dinner.
Oh, and Sanji's converted the Germa snail ships into a franchise of sea restaurants making sure no one starves at sea.