Nausicaa.net reports that Hayao Miyazaki is “entertaining” the idea of a sequel to Porco Rosso, also known as Kurenai no Buta, about a WWI ace pilot who gets cursed and turned into a pig. The film is also based on Miyazaki's manga Hikoutei Jidai, Age of the Flying Boat, although it's a much more light manga in tone compared to the movie. For the record they talk about him “drawing” the sequel, which I'm thinking means he'd be doing a sequel manga...but there's obviously drawing in an animated film as well, so who knows?
The news comes from a site about models (as in scale models of, say, WWI fighter jets, not those scrawny goofballs on a catwalk), Model Graphix, which reports that a model creator, Logan Umemoto, went to the Italian Air Force Museum to shoot reference pictures of a Caproni Campini for the movie. According to the Model Graphix article, it's only after boarding this particular plane that Miyazaki will draw the Porco Rosso sequel, and no one knows if or when that'll happen.
I dunno how there could be a sequel anyway. Didn't everyone die at the end? Or, wait, that was Pigs in Space. No? Um...hm. Babe?
...Okay, okay, I give up!