I don’t understand how ActivityPub works that well and I haven’t used Threads so maybe I just doing get it.
But why would we have to worry about defederating Threads when it’s a Twitter clone? It doesn’t have communities and such so I would think it’s not compatible. We’re not federated with Mastodon instances right? This seems like something for Mastodon to worry about. How is a Lemmy instance refusing to federate with Threads relevant?
On mastodon, you can subscribe to communities on platforms like Lemmy, the community looks like a user. On that side of things, it just acts like a relay that accepts messages and then sends it out to everyone who is subscribed.
However, your thoughts are on the right track. You don't really see that many Mastodon users on lemmy.