I don't think so. Currently , he only holds the rank of captain in the marine and luffy is already a well-known pirate in the new world. Assuming coby actually reaches the rank of admiral one day , the strength of luffy i think is already out of this world.
But this fight will not happen anytime soon. Oda recently states that he will end the story in another 10 years time . I wonder if it is true? since he said the same things 10 years ago.