@fediversereport my belief is that the opt-in requirement is so that Meta can use their policy clout to ensure that we end up with a "closed open" regulatory regime like the phone networks: you *can* federate, and the system is "open" but so highly regulated "for safety" that only large corporations can even imagine doing so, and in practice the whole thing is run by duopolies or pseudo-cartels (e.g. in the US: Verizon, T-Mobile, AT&T).
This would suit Meta just fine.