It'd be entirely open to Meta to simply turn off federation, in the same way that Truth Social and Counter Social have.
But honestly if I were them, given the hostile reaction I'd probably just do that and knock the whole ActivityPub thing on the head. It feels like a waste of time when realistically they would get more people on Threads/P92 in one day than a million Musk-buying-Twitters could do with Mastodon. Then everyone is happy - no Meta on fedi, Meta gets its new exciting Twitter clone that it fully controls.
Put it this way - either they're up to some form of non-specific evil, in which case they can probably achieve whatever goals they have far more concretely if they fully control the content on Threads, or they're not and all this is actually in good faith, in which case they're doing this for the benefit of a few hundred thousand fedi nerds who have reacted mostly with hostility and are going to block it on sight.
Nothing, which should probably raise concerns around how good a standard ActivityPub actually is if all it takes to drive a truck through its intent is one bad actor.