Besides, it's just so unimaginative to assume she's just something we've already seen. True, Moffat does return to the same wells rather often, but for now I'm willing to give him the benefit of the doubt and believe he's come up with something less obvious.
I'm beginning to wonder if Clara might be what the universe does without the Doctor. He's going to lengths to unmake himself, and the void that was the Doctor must be filled. As the Master said, "A universe without the Doctor scarcely bears thinking of."