This was really fun to do xD
Let's just say that this is what would have happened if Rainbow Dash had lost the race against the bullies in Cloudsdale.
You can see this anyway you want to, but the way I see this is:
Rainbow Dash loses the race and everypony makes fun of her for it. She tries to prove that she isn't a bad flyer, and in doing so hurts herself many times. Eventually, she breaks her right wing so much that she can no longer use it, and she is grounded forever.
Twilight Sparkle isn't enrolled into Celestia's School for Gifted Unicorns, and she works harder and harder to get herself enrolled. She eventually resorts to practicing dark magic, and she becomes possessed, and works to help King Sombra take back the Crystal Empire when it returns.
Pinkie Pie never becomes happy, and she stays at her family's rock farm, eventually becoming depressed and quickly angered.
Rarity soon discovers her magical ability to find gemstones in the ground, and she gives up being a fashion designer to become a jeweler. This makes her and her entire family incredibly rich, and she moves to Manehattan when she becomes older.
Applejack continues to live in Manehattan with her aunt and uncle and eventually learns how to act like "a true Manehattanite", and acts like a typical rich pony.
Fluttershy is ignored by the animals soon after Rainbow Dash loses the race. She returns to Cloudsdale, eventually returning back to the ground when she is older. Unfortunately, she is not able to support herself and make money, so she just lives out in the wilderness and learns how to heal animals.
I hope you guys like this!
All bases by: SelenaEde