No need for a new category... the notion itself is ridiculous. Are Sci-Fi geeks really pining so badly for an Oscar for one of "their" films? Do they need that validation? I don't. I'm just happy to see a good film from time to time. Hell - be happy we're going to see Avengers, Dark Knight, and Prometheus this year. I'm a hell of a lot more excited about that than I am the prospect of someone getting a little gold man.
If someone ever creates a Sci-Fi film that deserves an Oscar more than all the other films that year, it'll win one. Win because of quality, not because the suits created a little sub-award to placate you.
PS: Avatar didn't deserve a nomination, much less the award. I think that was a gesture for making a couple billion dollars while hitting all the correct political points.