Yes, this is what I was talking about with sys.config.
I meant it to be “readonly” just for users who are not familiar with releases as this might be a foreign concept for them and treated as transpiled build time mix config, fallback from runtime config as you mentioned. But of course if you know what you are doing, it is are editable and perfectly fine. If they want to do runtime config (and probably should) they need explicitly design it, ideally with the support of stdlib.
The only thing to state clear to Elixir developers is when building a release, mix config is compile time and any dynamic code will be evaluated at compile time. I don’t see it as an issue to be honest. A similar problem exists with module attributes, they are compile time and as far as I know we don’t try to fix them but rather educate people:
“Every time an attribute is read inside a function, a snapshot of its current value is taken. In other words, the value is read at compilation time and not at runtime. As we are going to see, this also makes attributes useful to be used as storage during module compilation.”
Source: https://elixir-lang.org/getting-started/module-attributes.html
