On the Lemmy and Kbin Magazine side of things, Threads won’t be a huge threat as most discussion will stay on existing communities/magazines, and most of the same users will be there with some interaction from Threads users.
On the Mastodon and the microblog side of things Threads will be interesting and I think the healthiest option is some server disconnect from Threads and others don’t. What you don’t want is ALL the discussion happening on threads and within threads, Threads should be set up as a gateway to the rest of the Fediverse despite the size difference.