Would be cool if people could not only subscribe to individual users via ActivityPub, but also to a group of blogs.
The reference implementation for that is probably Lemmy, but Soapbox/Pleroma is also working on groups support.
The reference for Lemmy’s implementation can be found here.
Thanks for bringing this up! This is absolutely something we’d like to address, and it was the original reason for developing our Pherephone project. That was built as a standalone app so it could be more widely useful, but it should also be possible to integrate it directly into WriteFreely. I think we just need to see some interest from developers who’d like to help with that effort.