I would consider developing this myself, but I not only lack the time, I also don't have any coding ability.
However, I personally believe that this could be an exciting project for someone with the right skills and interest in both the Fediverse and creative writing communities.
Presumably for the same reason you're on a federated forum-like platform: to have your posts syndicated to other websites for easier discovery, and to comment on posts from other websites without needing abother account?
IDK, I'm here on Lemmy basically as a refugee from Reddit, but the federation angle doesn't seem to help much from what I can tell. Look at how fast Bluesky overtook Mastodon. Anyway, anyone putting up new fanfic servers without understanding the politics and drama behind the existing ones is probably in for some pain. There used to be a saying "you're looking for a Star Trek solution to a Babylon 5 problem".
Royal Road has its own issues such as author groups on Discord colluding to drive up member’s “Rising Star” rankings, and drive down the stories of authors they don’t like. Also, very inconsistent moderation policies that highly favour certain authors over others who just so happen to be friendly with mods, etc.
I also don’t believe it’s open source, so I’m not sure how it’s really any “more free” than any other fanfic platform out there in the fediverse sense.
misskey is the closest thing to a federated tumblr. i dont know what the benefit of a federated ao3 would be since most fics are rather long and most wouldn't fit in in a microblog format.
besides ao3 is great as it is and they deserve support
I mean you could use pretty much any federated blogging software for such purposes.
The clue what ActivityPub is for is in the name: it is for publishing one's activities (so that others can subscribe to them). Fiction writing isn't inherently about publishing one's activities, the main thing you want to do on such platforms is host the content so others find it, not make sure your subscribers are notified about your activities. So it's not really clear how ActivityPub fits into that use case, although I suppose you could use it to publish the content.