There is a rumor of a spin-off where Princess Celestria sends the girls to Earth on a mission where they take the form of high school girls.
It was just considered a rumor at first, but it was backed up by a report in a trade magazine and an insider at the Hub.
Before you pony fans scream bloody murder, it is still in the rumor stage. Beisdes, it will be seperate from the show just as "All Grown Up" was seperate from the "Rugrats".
I still would like to please read your comments on the matter.