It's altogether too close to the Warlock.
Who offers mortals untold power in exchange for unspeakable things: Otherworldly Entities, Fey, Devils, Demons, Great People Who Are Dead, Shadow Beings and (ironically) the Sorcerer King.
Who does weird stuff with mortals so that some of them end up with magic in their blood: Otherworldly Entities, Fey, Devils, Demons, Shadow Beings (Great People Who Are Dead and the Sorcerer King could just be your ancestor already) - oh and Dragons.
No, I'd much rather have magic ITSELF empower the sorcerer than some bloodline. Let's have elementalists imbued with living fire or ice, and astromancers born when the stars are right, and wild mages who are accidental conduits for awesome power.