well i already mentioned a theory about him beeing some kinda hero
by kidnapping the mermaids he unwillingly protected them against luffy destroying fishman island.
maybe somehow he'll join the crew but with an hiddden agenda getting luffy's head like flare blitzz said
maybe oda will make it like a comedy (he tries but never succeeds)
i don't like that idea thoug,... you never know with oda