This story is a sequel to Accelerando
The ponies calling themselves the Bearers of the Elements of Harmony (along with the lowly Vinyl Scratch and Spike the Dragon) awaken from their long artificial dream. In truth, they are the most powerful ponies in the world of the far future. In this seemingly perfect world, the only problems plaguing ponykind are in their dreams, and that makes The Mistress of Dreams the de facto ruler of Equestria.
But all is not rosy in Ponyopolis, and the only way out of this growing nightmare is by sacrificing one of their own...