Here's my prediction for mastodon:

* wave of new users, most will go back to twitter
* enough will stay to keep things interesting and development will proceed apace.
* Valid feedback will be iterated on. instance-independent Identity, federated search, instance migration, performance tuning and bug fixes, etc.
* As it matures, it will grow.

Ultimately, a focus on keeping the community welcoming and easing the barriers to adoption will pay off.