Too late, IMO. The invite-only system meant that the "leave Twitter" crowd split between Threads, Bluesky and Mastodon. IMO none of them have ended up being great replacements.
Does anyone actually use threads? Everyone seemed to go check it out, but I don't know anyone actively using it.
For now, it's the most viable alternative for Twitter - for now.
But this is in part because Mastodon UX is very complicated for beginners, and BlueSky is slow as hell to make improvements. It still doesn't support sending videos...