I'm currently working on a prototype that does exactly this (in our case, the Gleam is essentially a typed calculation module wrapped in Elixir's great libraries for network and database interactions but its all net-new application instead of an existing Elixir codebase). Its not yet perfect, but I've been eagerly following along with this PR: https://github.com/elixir-lang/elixir/pull/14262#issuecommen...

Seems like (one of) the next Elixir releases will include the support you're looking for in mix.