I have 3...or 4 theories...



Theory 1...Ash Wasteland...Celestia went Knightmare 'Sun' on the world...



Theory 2...New Villian of Season 6



Theroy 3...Candice and Shinings new baby...the preview showed an insane storm and the fact their baby can shoot kamehameha beams with its horn...XD



Theory 4...Magic disappeared. Ponys use it for everything...Earth Ponys cant use it but plants grow around them alot more...Pegasus CONTROL the weather...and The Alicorn sisters rotate the planet since it cant seem to rotate itself.(Sure they SAY sun and moon ,but first HOW would that work considering gravity, and second HOW can Celestial move BOTH if the moon isnt even her domain?Answer:They are turning the planet itself like flipping a pancake to heat one side at a time.) now...imagine no assistance to plants growing,weather out of control,and a planet that no longer spins...Wasteland could happen that way o.o