Would you consider Erlang to be a proven language?
You can't hire or rent devs that know Erlang without a multi-month search in most markets. This is a non-starter for most businesses.
Train them on Erlang yourself? Why? Any possible productivity benefits offered by Erlang over a more mainstream option are dwarfed by training and hiring costs.
Nobody gives a shit about hot code patching in real business systems; the telco switch architectures which demanded such features are basically bonkers and unnecessary in a packet-switched world.
From my (limited) Erlang experience, Erlang & Elixir have the same core functionality. Elixir has a "nicer" syntax (I prefer Erlang's syntax but most devs I've talked to like Elixir's).
So if Elixir isn't proven but the concurrency model & programming paradigms make sense, maybe Erlang is a good choice.
* WhatsApp Scaling to 1 Billion users in erlang: https://www.youtube.com/watch?v=c12cYAUTXXs * https://www.erlang-factory.com/upload/presentations/395/Erla...
Erlang is proven in production for server and telephony apps.
> "From my (limited) Erlang experience, Erlang & Elixir have the same core functionality."
Depends on what you mean by 'core functionality'. If you mean the functionality provided by Beam VM or OTP, then there's a case to be made for that. However, the library ecosystem for Elixir is separate from the one for Erlang.
To use an alternate example, Java is definitely a 'production ready' language for enterprise software. However, if I write a new language for the JVM, it's not automatically 'production ready'. In most cases it's the library ecosystem which is under evaluation, not the platform the language runs on.