Another pony book has popped up on Amazon, though the title quickly changed on it. A cached page on google reveals "Welcome to Rainbow Falls". The synopsis sounds like it would be a lot of fun:
Tour another awesome area of Equestria as the ponies attend the famous sporting event known as the Equestrian Games in this fun storybook illustrated with artwork from the hit TV show. Includes punch out postcards!This one only clocks in at 24 pages, so it's not one of those massive chapter books. I guess only time will tell on what exactly it contains.
Thanks to Whathisgame for the heads up.