@Gargron I agree that this is overall a good thing for ActivityPub and for the widespread adoption of the vision you have championed. Facebook is validating the work you and others in this community have done. As Oscar Wilde said: "Imitation is the sincerest form of flattery that mediocrity can pay to greatness."
That said, I can assure you that Facebook has zero intention of supporting interoperable anything, ever and will work from within to destroy anything like that from ever happening.