I haven't read the rest of this thread yet, but one of the ones that I have been using for a while are a reinterpretation of the Yuan-Ti
Millenia ago the Yuan-Ti people came upon a heavily wounded and dying Snake God. The god, knowing it would die, offered its body and blood to the Yuan-Ti, who were fleeing some great threat. Upon eating it's flesh and drinking its blood they were transformed into the forms you are familiar with.
But, the Yuan-Ti also learned that this god had only been a fragment of a much larger and more powerful being that had been shattered. The Cosmic Serpent. Grateful to their savior, they sought a way to restore them and reasoned that if the divine essence that had been diffused among them could be concentrated, then the God and eventually the Serpent could be restored.
So, they began a culture of ritual cannabalism and a caste system. Upon death, a body is consumed and also during certain religious holidays and ceremonies, volunteers are asked for or voted on. People can refuse, it is an honor to be chosen because it is the community saying "your divine essence has reached a peak worthy of being ascended to the next tier" but if the individual feels it is not yet their time, they can refuse and the community accepts. Eating an unwilling sacrifice is blasphemy of the highest order. I don't think there is a higher crime in their culture. Second highest "bad thing" would be leaving a body to rot. Though, sometimes, that is a rare punishment for those they feel have defiled the divine essence in their body, allowing it to diffuse back into the earth to be re-aqquired later.
The Thinbloods (because why in the world would the lowest caste be called "pure") generally eat and devour snake meat during these ceremonies. Snakes being the essence of the god which fell into the sea and earth, and was not taken in by the people.
The best and most honored of the Thinbloods are devoured by the Half-Bloods, (The Malison in the book), who are the nobles and leaders of the Yuan-Ti.
And the Best and most honored of the Half-Bloods are devoured by the Pure Bloods (the abominations in the book, because again, why would the best caste be called abominations) who are the royal court and their direct relatives.
Then at the very top, is the Divine Emperor. An immortal who is to be the reborn God when his divine essence has returned to him.
And the subversive thing is... there is no subversion. This is how the system works, and they are right that it will work, and there is no corruption or secretly evil plots baked into the system. Are there those who do evil within the system? Sure, that's why the high punishments exist, but this is just how their culture and their people work, and they hope to one day have the purified Cosmic Serpent return and continue its divine mission (whatever that was, I haven't decided)