Looking at several recent demos where you could import your progress to the final version. (Etrian Odyssey IV, Dragon's Dogma) It seems like a good choice for a demo to the game.
Maybe a demo that goes through the first gym with a level cap on all Pokemon to prevent power leveling early on. This way everyone gets a feel for the game and playing the demo has purpose as you aren't just playing a pre set up party through a pre set portion of the game. Release it in September to hype people up for the October launch.
Know Japanese? Post your advice in the topic below! http://gamefaqs.com/boards/316-gamefaqs-world-japan/63714709