Sure, sounds cool. Have you finished the story? If not then what are you waiting for? Get to writing it! LOL. Actually, I'm only half kidding. It sounds like a neat concept, though it's impossible to really judge a story from a blurb or even a detailed outline.
The only thing I can say is to watch out for the hybrid concept. A hybrid with all the strengths and none of the weaknesses of both species is, in my opinion, boring. Blade is a good example of this. I think it'd be cool if your character found that his demonic powers weren't up to par with a fullblooded demon, and likewise that his magic was limited compared to a pureblood wizard. (Maybe not necessarily weaker, but limited perhaps to darker spheres of magic because of his demonic nature.) Anyway just my $.02.
Again, though, a cool concept isn't much without a story behind it. So I suggest you write, write, and then write some more. The board rules prevent from posting stories but there are a lot of online writing groups you could check out where writers swap stories for critique.
