Threads presents a serious danger to the long-term viability of the fediverse if we become dependent on it for content, and our best bet at avoiding that is defederation.
If Threads federates... it's part of the fediverse.
Even if you don't accept that tautology, sure, maybe the fediverse (not including Threads, which is also fediverse at that point, but ok whatever) doesn't do great, but kbin will definitely suffer if it defederates from Threads, once Threads becomes part of the fediverse federates does whatever you think it'll be doing that's not exactly the same thing as joining the fediverse and therefore becoming part of the thing that you think will become non-viable after the most viable piece of it joins. Kbin will become an also-ran within the fediverse, because most users will want to use tools that allow them to interact with the most people.
I guess what I'm saying is you can't in one breath say that "Threads will join the fediverse" and then in the next breath say "the fediverse will become non-viable" as if Threads isn't part of the fediverse in the second breath. Let's not do "separate but equal" with social media, please. It's silly.
If Kbin defederates from Threads, it'll be Kbin that suffers.