I collection of facts from Lauren Faust:
-Canterlot was intended to be a Gondor for little girls.
-Celestia and Luna’s parents were going to exist, but just wasn’t included.
-Twilight Sparkle was inspired by Lauren’s mother.
-Fluttershy was inspired by Lauren’s childhood.
-Pinkie Pie is NOT intended to be the ‘Random Character’, but a free spirit.
-Rarity was originally supposed to have a more British-sounding voice, but it evolved into what it is now.
-There were supposed to be 3 Scootaloo episodes spread across the 2 seasons.
-Scootaloo’s episodes revolved around the idea that she was technically a handicap; she would never be able to fly. They would be about the conflict between her wanting to be like Rainbow Dash and not being able to ever achieve that dream. In the end, she would discover herself and that there is a difference between what you want and what you’re actually good at; your destiny (her cutie mark would have been scooter-related).
(I want these episodes)
-Before Derpy was acknowledged, Faust already had an idea for a background character who would be a clumsy troublemaker. She would have been named ‘Ditzy Doo’. However, they are NOT one and the same. If Derpy had not come into being, Ditzy would have been made anyways. However, when Derpy happened, she took Ditzy’s place in Equestria. Both characters were simply supposed to be gag characters without a voice.
-Lauren came up with the concept of the Changelings, borrowing from mythology, but she did not draw or design them.
-A cut episode involved Rainbow Dash and Applejack encountering a deer family in Whitetail Wood, and a pony living among them. This pony would have had branches tied to his head because he was abandoned as a filly and raised by a deer. It is unknown whether the deer would have been sentient or not. The conflict would have been between Dash (who would have wanted to reveal the truth) and Applejack (who would have wanted to leave well enough alone).
(nice honesty there, Applejack. I also want this episode.)
-Lauren Faust (MLP:FiM, Foster), Gennedy Tartakovsky (Dexter’s Lab, Samurai Jack), Craig McCracken (Powerpuff Girls, Foster), and Rob Renzetti (My Life as a Teenage Robot, MLP:FiM, Gravity Falls) were all roommates in college.
(knew about the first three)
-Lauren and Craig are working on a new animated show titled “Wander over Yonder” which will be on Disney.
-Lauren was surprised that MLP:FiM has ended up where it has compared to Powerpuff Girls. The difference in popularity is likely because of the Internet (it wasn’t nearly as big or accessible back in the time of PPG).
source
Lauren cannot confirm or deny that she said these things. but I choose to believe them.