All forward looking statements are guesses but... I see a strong movement toward Elixir from Ruby devs (and others, I'm not a Rubyist) and I expect Phoenix to be one of the main frameworks in the next few years. It's due to a combination of simplicity, history (erlang is old), and a change in the types of apps some of us are building. There will always be simple CRUD apps too but the demand for constant connectivity seems to be rising. IoT, desktop replacement apps, etc.

Edit: fixed typo referring to Elixir as a framework