Who do you think will be the endgame villain for Luffy? Do you suspect an all out battle between factions is how OP concludes?
I’ve written about this in depth before, though heck if I can find it. My guess is that there will be kinda of a 2 to 3 part climax for the story. Because the story won’t end when the Straw Hats make it to Raftel–there’s so much stuff that needs to happen after that too. With Whitebeard’s dying moment’s, Oda foreshadowed that the discovery of One Piece will shake the whole world (see here). The corruption of the World Government has long been a major theme, and I am positive that it will collapse–or at least all it’s leaders will go down and more benevolent forces will take the helm–at the climax of the series. However, I do not think this is possible BEFORE the Straw Hats find One Piece. Roger left behind One Piece for a reason, so One Piece itself won’t be the end of the series. Rather the end will only come after the intents and world wide repercussions of One Piece have come to pass.
So my expectation is that there will be a penultimate battle with the Blackbeard Pirates on or immediately before reaching the island of Raftel. And after that, with One Piece’s discovery, the truth of One Piece, the final battle against the forces of the World Government, high likelihood of the involvement of the Revolutionary Army and other big forces, and a complete change in the power structure of the entire planet will constitute the final climax of the series.