The Spear of Elbaf
I had seen someone mention that Luffy may gain a powerful new ability in Elbaf related to the Spear of Elbaf. I don't recall the entire theory this other person had, but this was a very intriguing idea.
I agree that Luffy may add a new weapon to his style of fighting. I don't see why he couldn't especially if it was gifted to him or something and a giant happened to mention that Nika wielded a Legendary Spear which he focused his abilities through to great effect.
Let's say a certain conversation happens, and Luffy is told by a giant that unless he uses a weapon he will be unable to overcome Shanks who they are already familiar with. What if they said he can't overcome the Divine Departure unless he uses a similar technique? Then he'd be required to use something.
That's about as much as I'd like to say about it. I'd like to discuss Luffy making it change shape or something, but I don't want to get into discussions about how he should be able to take a toothpick and make it huge when he chomped on a tree to make a bat that didn't change shape before.
It's a bit of a tricky idea, but I could definitely make sense of a character hyping the Divine Departure to high heaven suggesting that it can't be countered unless someone uses something like it.