Earlier quoted context omitted.
At the core there is a custom crawler written in Rust, with the goal of eventually releasing it as an open source standalone application. But everything else, including scheduling the execution of this crawler, and parsing its output, is done on the Elixir monolith.
Would that be in Rust for performance reasons? Elixir IME isn't as slow as some other popular languages but it's no speed demon either.
Erlang/Elixir is good for networked servers. For CLI apps I either choose Go or Rust, and I much prefer the latter. Since I want to make this component open source, I wanted to keep it separate from the rest of the closed source, proprietary Elixir backend.
There is no wrong choice to be honest, this is mine for my startup, and I don't think I need more justification than "I am productive with it for the task at hand."