Just the fact that lemmy/kbin exists and that we are on it suggests that the scenario is unlikely. Still, the idea would be that Meta would make their own ActivityPub based service. They make it super easy for facebook/Instagram users to join. Then eventually they roll out some feature that needs MetaPub, their new open source (if you agree to their strict license) version of the api. Now if you want to interact with people using those features, you need to go to a Meta approved instance. Eventually they disable the old ActivityPub system and cut ties with standard Lemmy/kbin instances. Probably in the name of security or user experience.