Mastodon doesn't need to be "adopted by the masses" to be successful. I and plenty of other people are perfectly fine happy with it (and I use Mastodon comments for my blog.)
I don't understand the knee-jerk reactions whenever Mastodon comes up here. Someone always has to declare it dead, someone always has to rant about "leftist politics" and "fascist moderators." And then they usually suggest Nostr which is far more dead than Mastodon.
Nothing is perfect - Mastodon does have its rough edges - but even a moderately successful breakaway from mainstream social media is worth celebrating. I remember when the consensus on HN was that any alternative to the mainstream would be impossible, doomed to fail. The fediverse has its community and its identity, it isn't a flash in the pan.
Of course, if you move the goalposts far enough you can say any result is a success. Mastodon looks to have around 800k active users. For comparison IRC has (according to netsplit.de) around 280k users. Is that successful?
Same sentiment when it comes to Emacs. As a percentage, its use is generally constant or dropping. A tiny fraction of folks use it.
Yet in absolute numbers users are increasing. And Emacs activity is greater than it has ever been.
Yes. You don't need mass adoption to be wildly successful!