Makes sense, it was already open source, just attaching to the activitypub protocol is a straightforward move.
It’s everywhere too. Blogs, webcomics, special interest forums, and they will all potentially become new fediverse instances virtually by default. It’s pointing to a future where people join the fediverse without knowing what it is or seeking it out. They just want to join a forum to discuss their interests.
It could be an issue if the admin isn’t prepared for it. One of the good things about it is that the posts get cached wherever they’re accessed so it may actually reduce server load for a popular post.
I guess if it is an issue the admins could always disable activitypub.