Look if you want to run something like that, then go for it, nobody is stopping you. But we've had a bunch of threads like this already and srsly, the software is not an issue. The reason AO3 came into existence in the first place was to create a home for stories and authors that kept getting banned from other sites. It's about the stories and content policy, not the software. Do you think a federated version will allow those stories? Will your own instance allow them?

I'm not into those kinds of stories myself (by far the biggest Harry Potter category there has Harry dating Draco), but the fact that they are allowed contributes to the tolerant atmosphere of the whole site. It was similar with Reddit before it got too corporate, and to some extent even now. Lemmy is ridiculously stuck-up by comparison. I don't understand why people think federation (Lemmy style) is some kind of fairy dust. It operates the wrong way imho: stuff like subscriptions should be entirely on the client side, to get rid of the choke point that exists at every interface between two federated servers.

The name "ourchive" is cute but I think it's too imitative of AO3. So I'd hope for a different name. But, props for cleverness.