The spirit of Harmony reveals to Twilight that a new generation of Bearers of the Elements of Harmony will be gathered soon. Nobody, not even Harmony itself, could have guessed just how soon that gathering would need to occur.
The Order-naries arrive a little too late to take part in the main plot of the MLP Movie. Saving Cadance from the Storm King and making a run for the Crystal Empire by train should make for a fine substitute adventure, though.
It's hard enough just being a new Queen of the Changelings: teaching the Hive new ways to live, dealing with pony politics and plundervines, staging a musical... Try doing all that while also trying to put the old, hated Queen back on the throne
Cabbage Patch is a Changeling who just wishes to live as a pony, to forget about her past and live a somewhat normal life traveling and performing with Trixie's Thespians. Fate, and a certain Princess, have other plans for her though.
The Order-naries are back in Equestria and quickly find themselves embroiled in a disturbingly familiar adventure alongside some VERY disturbingly familiar faces.