then they’ll find some sort of technical excuse and pull the plug on ActivityPub support

How do they do this without running a foul of regulators? People are already mad at meta and want to break them up for having instagram and Facebook, if they add the last big social media platform every politician right and left will be lining up to take them down. There’s a reason they never bought twitter despite being able to 10x over. Combine that with new EU interoperability laws and there’s no way meta could get away with that.