Well, that little Disney thing that spawned a huge Johnny Depp announcement also brings news of a National Treasure 3 so says IESB saying Jerry Bruckheimer, Nicolas Cage and Disney’s Dick Cook confirmed the film’s development.
The site says there are rumblings of a 2010 holiday release.
As for plot, there is none, but I think Ben Gates (Cage) and Co. should go out searching for the Fountain of Youth only to find it and discover Captain Barbossa and Captain Jack Sparrow and then move into a prequel story that will be Pirates of the Caribbean 4 that will leading into a National Pirates of the Caribbean Treasure spin-off in which they go in search of the real story behind the head of that statue in Miracle at St. Anna. Just an idea.