Personally, it’s the implausibility of 2 that makes all of this seem like no big deal to me. In fact, I think federating openly with Threads might signal to Threads users that they can use alternatives and not lose access to whomever they follow on Threads, thus growing the user-base of other federated instances.

I think people who are going to use Threads for Meta-specific features are likely going to use Threads anyway, and if any of those features are genuinely good (i.e. not simply Instagram and Facebook tie-ins) they will be replicated by the various open Fediverse projects which already differ from one another in terms of features.

The moderation issue is entirely different and there are some instances that have an understanding with their users about protecting them from seeing any objectionable content or behavior as defined by whatever culture they have. Defederating from such a large group of people makes sense, perhaps even preemptively, no different from when they defederate existing large instances now.