There's no plan to ever have a v2.0.
I think most elixir projects are on Phoenix, and while I can't speak too much about the speed of that project, the poster you're responding too has clearly stated they have an app that's 4 years old and running just fine so I have to believe it's not as much of an issue as you think.
There are some new choices for building releases that make it easier for people who prefer to use run time environment mentioned variables for configuration instead of compile time ones. Previous ways of building releases still work as before.
I make releases with Distillery just as I did back in 2016. The main change in my release workflow is that now I use Gitlab CI/CD, and that's unrelated to any Elixir or Phoenix changes.
I don't know what that means in this context. What I do know is that RoR versions go EOL roughly 2-3 years after they're released. That's not stable by any stretch of the imagination.