One thing I find interesting already about the choice is that Porco Rosso is by far Miyazaki's least-popular (read: least-seen) film of the past 25 years. It's typically more common for someone to return to a film that has a lot of fans or at least made a lot of money. Even I would prefer another go at the world of My Neighbor Totoro (hopefully gaining new fans through its Toy Story 3 tribute), for instance. But the good thing is this should make more people go and rent Porco, which is an exciting animated action-adventure about an ace Italian pilot-turned bounty hunter with the face of a pig. It also, to Disney's delight I'm sure (they distribute his films in the U.S.), has more potential to appeal to boys than many of Miyazaki's films before or since, which tend to have female protagonists.
Some of the translation of the interview is confusing, however. It seems Miyazaki's next film could actually be something with a female lead, while there's also some business about Ghibli going out of business as an animation studio if its upcoming adaptation of The Borrowers (which Miyazaki scripted), is not successful. Miyazaki admits that the Porco Rosso sequel idea is a "hobby of an old man," though he does have all the materials to get it going if he's given the go-ahead to do it. Whatever the case, you Miyazaki and Ghibli fans out there should be sure to see The Borrowers -- and for now, there's the just-released (on five screens) Tales of Earthsea, which could probably use some love -- so we can have as many future projects as possible from that team of animators.