because the term has associations that just don't apply to a work written by a non-human

Well, if the non-human produces something that for the audience is indistinguishable from something produced by a human, I'd say it's close enough. I don't think we usually know enough about the circumstances of production to be able to rely on that for a definition. With fanfic, of course, we have the fic that clearly is produced within the context of the community - but that only applies to the people we know to be in the community. Can we make that judgement about a random ff.net poster?