It's one of the first things I would expect from a site like this. I know that J.K. Rowlings views are very controversial to put it mildly, but:

1. The fandom/books are not the author
2. Harry Potter will become a part of the Fediverse at some point anyways - better to support it early on and shape its developing rather than having a company build a H.P. social network on top of the fediverse, which will be to our disadvantage
3. In terms of potential users, this could be huge for the threadiverse
4. We are in the Fediverse: defederation is always a possibility

Or was it just never tried before / no one wanted to yet?