@Nobodyman:
Well, that' just it. In a series like this where the main character has a long-term goal in mind, the story ends as soon as he/she accomplishes it.
One Piece will end when Luffy becomes Pirate King.
Naruto will end when Naruto becomes Hokage bones Sasuke.
And Bleach will end when someone puts a bullet in Kubo's head (was that dark? Yeah, that was kinda dark).
Likewise, Bakuman will end once Ashirogi gets their anime and Mashiro and Azuki hook up. Yeah, it sucks we won't get to see more of these characters and the awesome world of manga, but do we really want more dog boy and Nanamine arcs?
Aaaaaactually….context clues in the story don't really point towards One Piece ending at Raftel. At the very least the story cannot possibly end with discovery of One Piece. There is too much to the story that is left to be told AFTER Luffy has become Pirate King / Landed at Raftel. The true History, Will of D., and the Great War with the World Government all will come AFTER Luffy is Pirate King.
Also remember, the series is not just about Luffy fulfilling his dream, but also Zoro, Nami, Usopp, Sanji, Chopper, Robin, Franky, and Brook. Landing at Raftel only satisfies Luffy's, Robin's, and Franky's dreams. Luffy will find One Piece, Thousand Sunny will have sailed to the end of the Grand Line, and Robin will find the Rio Poneglyph....but it would be terribly cliche and non-Oda like to have Zoro face off with Mihawk, Usopp declare himself a brave warrior of the seas, Nami complete a world map (having just sailed the Grand Line), All Blue surrounding Raftel, Chopper discovering some miracle cure found only on Raftel, and Brook taking a quick run over Reverse Mountain to see Laboon again all at once.
Rather, I feel the straw Hats will complete their dreams one by one. I think Zoro's, Sanji's, Brook's, Nami's, and Chopper's will remain incomplete when the Straw Hats reach Raftel.
I honestly feel that One Piece will turn out to be a three-act story. I know Oda keeps saying halfway, halfway, halfway. He called Alabasta the halfway point. He also called Enies Lobby the halfway point. He also called Impel Down the halfway point. Most recently he's been indicating that the time skip is halfway. Honestly, the halfway point in the story must be traveling aboard the sunny because it seems to be moving with the story.
The first act, the Grand Line
The second act, the New World
The third act, the World Engulfing Conflict / War with the World Government.
This is a Bakuman topic...idk I don't want to go into details. I just think One Piece is going to end up lasting like another 20 years and totaling something like 120 - 150 volumes when all is said and done.
Also, I think Bleach will end the way Shaman King ended....just gets more and more boring and repetitive, looses popularity, and eventually gets canceled with no definite ending. Or it could end after the next few story arcs.
Current predictions:
One Piece - 1250 - 1500 chapters
Naruto - 650 - 750 chapters
Bleach - 600 chapters
Bakuman - 200 chapters or so (250 MAX...dont' see it going that much longer)