I was just thinking that Mihawk when talking to shanks mentioned that he is not worth fighting ever since he lost his arm. The arm was a major part of Luffy's past obvious and might be stupid of me to think of this from a narrative standpoint but what if shanks find the axolotl devil fruit. axolotl in the wild are known as a creature that can grow entire limbs back. I think that the rebirth of the axolotl fruit was not just too show the cycle of devil fruits but to show the audience that this fruit is now back in the cycle for someone else to use. If I remember shanks became a yonka post losing his arm, and this means that even though he lost an arm he was still strong enough to become one of the strongest people on the sea, but what if somehow he would be able to regain his lost arm. I may be wrong but, I don't remember off the top of my head writing this post but, it was either implied that shanks duel wielded, or it might have been a theory.