I see some merit in Ploum's argument that the same way the Google monolith slowed down XMPP development, Meta could slow down ActivityPub development or steer it in a certain direction by forcing others to implement their extensions if they want to keep interoperability, before finally dumping it. But yes the "extinguish" situation would then be a return to the current status-quo, Fediverse as a tiny niche of like-minded people doing their own thing.