I share the OP's enthusiasm for Elixir, but as the CTO of a startup that ran it for three years in production, our experience was a mixed bag as the codebase grew.

The core promises of the BEAM (concurrency, fault tolerance) absolutely held up. Libraries like Ecto and Oban are world-class, remote `iex` is a lifesaver in prod, and the talent pool is exceptional.

However, developer experience (DX) was our biggest bottleneck. At our scale of 300k lines of code, the pain points were sharp:

* Compile times: A one-line change could easily take >10 seconds to compile in dev, constantly shattering flow.

* Tooling: ElixirLS was a coin flip. Unreliable autocomplete in a large codebase meant constantly grepping for function names and schema fields.

* LiveView: It wasn't a fit for our complex UI, which required a lot of client-side interactivity, forcing us to build a React frontend. This introduced the exact split-stack complexity (GraphQL overhead, context switching) LiveView promises to fix

I wrote a full retrospective for anyone considering the stack for a long-term project: https://ryanrasti.com/blog/elixir-three-years-production/