I can't run the examples right now, but looking at the last "print(template.to_json())" line, looks like the main use case is JSON ?

On cloud infra, yes, having one or two layers of languages is a natural situation. GCP and AWS both accepting (encouraging?) JSON as a subset of YAML makes it a simpler choice when choosing an auto generating target.

You mention people wanting to author the generated files, I think in other situations tweaking the auto-generated files will be seen as riskier with potential overwriting issues, so lower readability will be seen as a positive.