I don't believe that federating with Threads will be completely apocalyptic, and I actually believe that the commercialization of the Fediverse is the way it will take over the internet. You can't run the entire internet on a crowdfunded and volunteer-only basis, after all. The beauty of the Fediverse is that competition is easy and enshittification is difficult due to how easy it'll be to simply take your activity somewhere else, meaning that companies like Meta won't be able to do the type of things they're known for.
That being said, I believe that for technical reasons, as well as the fact that it'd be very easy for Meta to strangle their competition in the cradle if we (Referring to the Fediverse as a whole, as this isn't even my instance) cooperated with them, nobody should federate with Threads until the Fediverse is large, resilient, and technologically matured enough to survive a hostile takeover attempt by a corporation like Meta. Basically, defederate from them for now, and reconsider at a later date when the Fediverse has had time to establish itself. I think in the future, the Fediverse will be able to easily deal with Threads being popular and enshittifying itself, but I simply don't think we're there yet.