My favourite AU hasn't been written yet. Severus decides to transfer to Ilvermony after SWM where people realise he's a genius and get him the help he needs. People notice how the new kid is jumpy and has his wand out as if he expects an attack. They break the oath he's under and are horrified to learn the whole story. He does really well in potions and spell creation. His ability with Occlumency gets notice and Queenie comes by, they talk excitedly and try to teach other their respective gifts.