I got a number of answers that sound very weak to me, and basically point to a "fail" of the fediverse in its own nature if threads joins. Kind of disappointing.
To me, the key idea of the fediverse is that it's federated and should work as a whole, no matter who joins. Most of the answers below support the opposite. They are basically saying that the fediverse should stay within the "fediverse", which is exactly what non-federated social media are doing. Meh.
https://lemmy.world/post/10678878