Well seeing so far how all the stories are always ending to have a great coherence (like skypiae with Jaya etc..), I made up my own theory about how some strawhat's goals will go to the same way eventually :
Althought Luffy and Zorro will surely go to the top together, I always wondered how something like Nami's or Sanji's could have a link to one piece, or to the One piece world.
With the recent news about the old Civilization, wich seems to be at the center of the One Piece world and story background, I think that :
The old Civilization actually IS Grandline, or to be more precise Grandline is what remains of the Civilization (This one was already talked about I think)
All Blue is today a legend is because it existed from the time of the civilization, and the world at this time was different : the 4 sees met together at the center of the world, till grand line was created (800 years ago perhaps?? :happy: ) So for Sanji to realize his dream, to find all Blue, the world will have to chance to what it was once, or to something else. (Seems now more epic than fishing in the 4 sees don't you think ??:biggrin: ).
In the same way, Nami could be the one to discover the true nature of Grand line : She is the first to try to do a global map of the world (or the first to be good enough to realize it), of her cruse around the world. She will also be able to see them (the maps) together, and, who knows, maybe some islands will just be like skypiae and Jaya (Foreshadowing? It wouldn't be so surprising from Oda..), they will do a coherent continent.
At this point, I can just speculate about what will happen : maybe One Piece is a way to change the world to what it was once, or it's the thing that created grand line, and it would still change the world to something else..
Maybe the Strawhats will have the choice to use it or not at the end of the story, choice between their dreams and the world.
In all cases I think that this theory have some sense globally.
Well I have many other ideas in my mind, you can go on with the others strawhats (but chopper, I didn't find a direct link here..), but it's kinda difficult for me to say it in english, I hope you understood me so far. Feel free to tell me what you think about it, after all it's just speculation ! :laugh: