It sounds like there are probably already enough similarities between PotD and Aquapolis to make something like this without too much difficulty.

The only concern see is that most (if not all?) of the Gold Saucer content is for everyone who can enter the Gold Saucer: level 15. The only exception I can think of is getting 100% on fashion report, but even level 15 characters can get significant participation points and play it. So something like this would probably either need to be synced or just come with a unique combat system instead of players' job abilities?