That ship has sailed. In the first few weeks there was lots of buzz about alternatives, PG had a little fit and spent about 15 minutes exclusively on mastadon etc. The buzz is gone now, something big will have to change for it to get it's momentum again.
Mastodon is doing just fine, from what I can tell. I don't know why people keep pushing the narrative that an alternative platform has to capture Twitter's userbase in its entirety or else be considered a failure. Not everything is driven by buzz and hype.
Mastodon is doing great. Just passed 10 million users a while ago and now has a sustained network effect of around 2000 users an hour. Numbers aside the community and experience is awesome. No idea how people still use Twitter.