Mastodon was dead from the start, it isn’t in the running.
Threads has too big of an image problem to overcome. No one wants Instagram for Twitter.
Bluesky is the only platform currently that has a chance, but it’s an under funded, tiny team who can’t ship on time. Bluesky will see a surge in registrations but no change in DAU as they still haven’t supported video, so no one will stay on the site.