I would imagine that the kind of people willing to use Threads were already not going to sign up for a “small instance”, and a lot of admins of various sized instances have already agreed to defederate regardless https://fedipact.online/

I don’t really see how it’d be a loss. The fediverse has existed for a long time alongside big centralized social media, and Threads ostensibly having ActivityPub support doesn’t really change that.