Really great documentation so far! As a reader, I was curious what "index.js" should contain, any hints would be appreciated. Perhaps something like Vue.mwCreateApp( { render: ... } ).mount( domElement )?
Topic on Talk:Codex
Yes, that's exactly right, init.js should contain code mounting the component. I've tried to make this clearer by linking to the Vue.js documentation page at the top of the Codex page, and also linking to the section about init files below the example that uses an init file.
One thing that I'd still like to find a place to add is an example showing how all these pieces come together into an example module. That would probably fit best on the Vue.js page.