By vaster I think he meant that the New World is drastically more imaginative and magical. In the span of a chapter we've already seen just how much more crazier the new world is compared to the old world.
And it really depends on how long One Piece's popularity will last. I forget in which interview he said it in, but Oda said he already knows how exactly to end One Piece and could have ended it already whenever he made that specific interview. Shounen Jump will try and ride out its popularity until the very end. A good chunk of people knew Akira Toriyama originally had Dragon Ball end after the Freiza arc, but did you know he originally originally wanted to end it after Emporer Pilaf? When Goku first turns into a giant monkey? The very very VERY first arc? Hopefully the editors don't piss off Oda too much like they did Yoshihiro Togashi whose limits were tested and axed Yu Yu Hakusho in the middle of the last arc abruptly. Though since he's their cash cow and it seems Oda enjoys creating vast and intricate arcs, One Piece could just as easily last for another 10 years...or more.
Actually yes that is what i meant, more imaginative and the arcs can be setup longer then the previous one, becauze it's very crazy in the New World and the people over there are much stronger. He can put as many pirate crews there as he want to encounter the straw hats. He will probably also fill the gaps of the Shichibukai.
Oda can still do so much and go so many directions for a lott of arcs. I also think they will ride out the popularity of One Piece, i hope it will last for a long time.