I really like the idea of an activitypub platform tailored towards writing, fanfic or otherwise. You wouldn’t need to specify because the various styles would probably gravitate to different instances.
I’m sure someone will pick it up eventually, because it just makes sense. I actually do have programming skills but no time to devote to something like this. I have no idea how much work it would involve but the general rule I have for things like this is “more than I expected”.