I don't see Mastodon becoming the next Twitter. It has a marketing problem. Whereas on Twitter one "tweets", what does one do on Mastodon, "masticate"?
I predict a temporary influx of new users, which will leave once they realise that Mastodon is full of shrill geeks. In the interim the shrill geeks will moan that their beloved platform has become overrun with "normies".
I don't use either so have no skin in this game, happy to be proven wrong. Sitting back with a very small bag of popcorn until all the noise blows over.