Gregory's ServerGranted, Threads isn't in Europe because it would run afoul of privacy protections, but they may not care. They may not care about joining the Fediverse ultimately either. They could seriously fracture the Fediverse if they do, however, as people come down on either defederating from its massive user base or trying to glom onto it. Of course, Threads could also fizzle out as Instagram users get bored with it.
But Threads has to make Musk nervous. (He's already firing off legal threats. LOL.)
Honestly, it should make everyone anxious about the future of social media being at the mercy of these corporate power players, who are only interested in creating pay-to-play walled gardens and harvesting our information.
Mastodon still seems like the best, to me, in terms of what I want from the experience. But it may remain a niche space, which I think is deeply unfortunate.