Starting a test where posts from Threads accounts will be available on Mastodon and other services that use the ActivityPub protocol. Making Threads interoperable will give people more choice over how they interact and it will help content reach more people. I'm pretty optimistic about this.
I think it validates the platform for normies.
I don't think people who are using Threads are or will be aware of Lemmy, Kbin, or future services that are Reddit-like with or without federation.
Lemmy federation with Mastodon and similar services is clunky at best. Kbin having the best cross service type handling as it focused on exactly that is indicative of how poor the federation of cross service communication is overall.
I think adding Threads to this mix is not going to be pleasant for users of either service or adnins of Lemmy instances.
I just mean it validates that the fediverse is important and not some random scam. It's both good and bad. But mostly good.