I like the interpretation of draconequui from this fun little CYOA: https://travellers-cyoas.neocities.org/MLP/

They're magical spirits that each have their own "principle" kinda like a god's domain. Discord looks the way he does because his principle is Chaos, but I can easily imagine draconequui with other principles being far more symmetrical and less chimeric. The only hard rule I'd set is the dragon+horse combo, since it's in the name.

Maybe the species is the result of an arcane experiment to combine unicorns and dragons? That'd be cool.