Close to 100% of my readings lists on DW and LJ use "fanfiction" or "fanfic" or just "fic". Having read the post on the OTW blog, I can't disagree with the TWC' editors reasoning, and if and when I ever write something about fandom for a non-fannish audience, I'll probably use "fan fiction" as per the dictionary spelling. But even as an academic in training, writing it out with two words just seems...odd to me. I think, for myself personally and within fandom, I don't personally feel a need to emphasize fan agency that way; it seems redundant.