Oops, I just did that, didn't I? ;-)

I guess all we've got is their word, but the writers have been consistent in their claim that they know where they're going, and it doesn't seem all that far-fetched to me. Something specific they've said is that there were some moments in Season 1 that, after the show is over, will make it clear that they knew where they were going with the story (I think the Adam and Eve bodies are supposed to be one of them). I guess we won't really know until the show is over.