I agree that one of the best ways to improve Elixir is to improve Erlang/OTP. There are many areas of OTP in particular that are unpolished/in need of some love. One area that is still not-as-good-as-it-could-be is the lack of Common Test integration with Elixir. Not that Common Test makes any of this easy to do, of course (it’s not designed very well to play nicely with anything other than Erlang/OTP; for example
_SUITE.erl is literally hard-coded in a few places).
In general, I think there are people within the Erlang community who wouldn’t mind moving into the Elixir ecosystem, but have a hard time because they have to give up some of the tooling and frameworks they’re accustomed to using to do their work. Common Test is one of those areas where I don’t feel like we have an equivalent available in Elixir.