We have user level domain blocking, so if you block an instance it's a bit like defederation.

Afaik you can still sometimes see their users on other instances but you don't see any of the blocked instance's own content anywhere.

I am not super familiar with it, but my understanding is that Kbin lets users block something by domain.

So, my understanding is that yes individual users could theoretically block Threads content.

If I am wrong, somebody please correct me!

I don't think so, only if you spin up your own instance. I myself have my own instance of Mastodon where I defederated Threads.

I don't think full instance blocking is available yet, just users and specific communities