I won’t list all of them, but there is one that is particulary relevant right now. I don’t know how you call it, but it’s basically what CartoonLion does to ponies in some of his/her(?) fanart: some of the ponies are turned into humans and live typical human lives, while others are turned into their non-sentient (or semi-sentient ) pets and are treated by them just like pets in our world. Can’t tell why but I absolutely love the idea that while in the series all the characters were more or less equal, here some of them are reduced to silly critters who focus mostly on food and play, while others basically get to be their legal owners. Like when in the series Pipsqueak is sad because there won’t be another nightmare night, but in CL’s universe, he’s Scootaloo’s pet pony. Or how Celestia trains Luna, her pet, to jump for a cookie.
And I know that some people would probably hate me for that, but here’s why I said this one is now so relevant. I won’t lie when I say that I like the idea of Spike the dog so much specifically because of this fetish, as sick as some people might think it is. As mistreated as he sometimes was, he was still equal to ponies despite being a dragon, but in EqG he’s the only one not allowed to be a human, wearing a corral, being Twilight’s pet and probably not even having human intelligence. Remember how in Just For Sidekicks he was saying to CMC “take it or leave it”? Basically four kids arguing, like kids tend to do, all of them equal. Now CMC will get to party with others at the school dance, while he will be a dog. I like to hope that we will see Twilight take him for walks, bring him to a vet and feed him dog snacks. Sometimes I even imagine that AJ will still have Winona and Spike will like to play with her even thought he used to walk her, but that might be a little too much to expect…