What nfic tells us is that the story is from the genre nfic. If we're trying to list fanfic by genre, then it seems to me that nfic is a fairly logical addition to the list.
Granted, it's a wide definition - but then so are most of the others in the list, because genre as a concept is pretty wide-ranging. And, yes, we could spend a lot of time breaking down these genres into different sub-categories, but that's another project, I think.
LabRat