Oda has been asked about the story ending! Here is what he says about it! one piece

“The story’s end hasn’t changed once since the beginning. The problem is that I haven’t been able to really digest all the things that are happening along the way toward the end.” Inoue Takehiko Pia(2009)

Question: …Exactly how far ahead do you plan One Piece, and what is your story-planning technique?
Oda: I only have the ending of One Piece in my mind, and nothing else. But knowing the end point, I weave the story and make story arcs that build up to it. English Shonen Jump

“I just can’t help but draw a lot. The weekly format is set at 19 pages, but from the creator perspective I want to move the story along faster. I end up jamming as much as I can in there. There is also wanting to finish faster so I can relax.” Inoue Takehiko Pia (2009)

“The thing I want to do most in my comics is really not stories, it’s character models. I think like, “Is this style of person possible?” The time I spend doing all kinds of different designs is fun.”