As much as I hate Meta, I don't think it makes sense to defederate preemptively. I personally feel like doing that would be telling Threads users "if you choose to use Threads, you aren't allowed to be a part of the Fediverse" which I think basically defeats the point of federation.
I also think Threads is a good entry point for a lot of people to experience the Fediverse and move to other platforms such as Lemmy or Mastodon.
That being said, if Threads proves to be a huge problem down the road, beyond it just being Meta-owned, then we can defederate. Otherwise, we should wait and see. I think the Fediverse is big and strong enough that waiting to see won't hurt us.