I certainly hope he joins. I've always liked his character and I enjoyed his backstory in the FI arc. I also like what his relationship with Luffy represents and just how much support he gave Luffy after the MF war. His friendship with Ace makes him even better and I think he would gel with the other characters. I used to think Franky wouldn't be a good fit but definitely don't feel that way now. I hope he joins but I have a feeling it won't be anything simple.