Why so you guys think One Piece is ending anytime soon?

I just caught up with one piece. I have put it off for years but I kept hearing that the end of the series was near, so I finally did it, but after finishing it I don't think it's ending anytime soon.

There is still just so much we don't know, like the blank century, the story of Joy boy, the ancient weapons and so much more. Also it seems to me like they're setting up for the straw hats to turn around and go back to the grand line.

Based on this it seems to like the series has about another 15-20 years left, but when do you guys think it will end and why?