Have seen the trailer, a bit greatly simplified, as it shows how envy arises in the earth ponies who discovered how the pegasi and the unicorns got great benefits with the return of magic; a sequel from exactly where the movie ended, when we saw the tracks of the earth pony foal. Traces of earth pony magic. And it also shows that the unity crystal can be hypersensitive to irregularities in the pony kind - and that the magic seemed to represent a latent danger that the ponies do not understand. It seems that imbalance opens up for unforeseen consequences, which the unity crystal can be meant to counteract.
At 0.19 we saw how the pegasi lost their magic, and at 0.21 Sunny lost control of her alicorn powers before disappearing. Then a hole appeared that appears to be a dimensional portal, at 1.10 just after a crack appeared on the crystal. Since Izzy could liberate others with her magic, it meant that active magic came from the hole to catch ponies nearby. In fact, on closer inspection, it turned out that only earth ponies were “caught”. Could it mean that the earth pony magic had been activated? In that case, the envy we saw in the trailer may have led to corruption. And when the pegasi tried to free the captured ponies, they got the magic back.
This indicates that the unity crystal has made the pony magic unstable, or perhaps it had become unstable after the end of the G4, and Twilight Sparkle may have made the three crystals as a result. But then it means that the magic in G5 is not reliable, so the ponies must have aids they would not have needed in older times. But Sunny eventually intervenes and makes use of her alicorn powers. In 0.57, Sunny was in total darkness, which indicates that she had plunged into the hole. And we know from an early recording that a rainbow ray came out of the hole.
Undoubtedly, she will discover the magic of the earth pony and show the dissatisfied earth ponies that they also have magic. It would be hysterically funny if they were to smash everything they touch and make plants grow uncontrollably, and find that they can manipulate the elements in the soil. After all, an imbalance must be corrected, and this seems to be Sunny’s job.
Hitch inherited Fluffershy’s talent and the dragon egg appeared to have been found before the drama broke out. With the return of the earth pony magic, the egg can be broken so the dragon will come out into the world. We know from the G4 that the earth ponies and dragons had a complicated relationship from open hostility to indifference, but also that they are “down to earth” in comparison with others.