After thinking about it, and reading other peoples posts, i also hope that he doesnt have a devils fruit. As someone put it (sorry cant remember name now) it should be a man and his sword vs a man and his sword. Nothing more, anything less then his title should be "The Worlds Greatest Swordmans with a Devils Fruit" instead of just the worlds strongest swordsman. He should be able to take Devil Fruit users and those without, the worlds greatest, I really hope Oda doesnt give him one.
Anways, back to the theories! Hmmm, while in school (half way sleep) I was thinking about a possible time jump, it almost has to be one, I really dont want Luffy to be like 19 years old and the Pirate King at the end of the series. Especially with people like
spending there whole lives searching for it.