First off, Koby has appeared twice. He was there in the marineford arc. He actually stood up against Aikanu to make him stop the killing. Then Shanks saved him from death, remember?
And later we saw, that he became able to use Haki.
That said, I still see Smoker as the eternal enemy from the marines. He has been hunting Luffy ever since day one. Koby is behind Luffy, he will most likely never catch up to him in strength, so I am not really sure about his role, but I could see him ending up as a very powerful marine one day, although Aikanu does not give much about him
And later we saw, that he became able to use Haki.
That said, I still see Smoker as the eternal enemy from the marines. He has been hunting Luffy ever since day one. Koby is behind Luffy, he will most likely never catch up to him in strength, so I am not really sure about his role, but I could see him ending up as a very powerful marine one day, although Aikanu does not give much about him