Oh, absolutely. Even amongst all of the large servers, which expect to allow federation with Threads, none of them intend to give Meta special treatment. If they can't keep their house in order, they will end up getting defederated.

That being said, the big question will be how open Threads is to the rest of the fediverse. It likely won't include the global federated feed, so the question will be how much Threads users end up interacting with the average Mastodon user. It might end up being we only see Threads users when they either manually know a user they want to follow, or Meta promotes content from folks like George Takei into Threads and we see trash comments on that.