Fediverse will go through what Linux went through. Be seen by businesses as an existential threat. Then face FUD and EEE campaign.
One day, likely earlier than Linux witnessed the rise of RedHat, Google, Facebook as prominent businesses that became poster children for Linux, new or existing businesses could be built around and/or on fediverse. They may as well come together to form an ActivityPub foundation similar to the Linux Foundation for all we know.
Email went through similar trajectory too. SMTP, IMAP, pop are are open protocols. Yet we have a sort of oligopoly on email.
Similar to how Windows did not die away because Linux came along, existing social networks may remain in existence. The availability of fediverse as an alternative would keep them busy