I'm probably betraying a shocking degree of ignorance regarding intellectual property law here, but on what grounds? Fan fiction is, by definition, a derivative work and can be suppressed at the whim of the creator or whatever entity owns the rights to the property it's based off of, so it doesn't seem to be covered by a fair use exemption. Does a copyright still attach to works that are themselves
a violation of another copyright?
EDIT: I went sniffing around Wikipedia and looks like the answer to my question is "it's protected as long as it displays some originality of its own" which most of the fics discussed here probably do. So my understanding is that fanfiction can be suppressed but not stolen.
It already is a thing. And the story I mentioned earlier, Contraptionology, is very much in the same spirit as Girl Genius
EDIT: Because 'a shocking lack of ignorance' just sounds like a really pretentious way to claim that I know what I'm talking about