This plugin is already good to create themes for live production sites.
The disclaimer “The plugin is for development only — it is not intended for use on production websites, but to be used as a tool to create new themes.” means that you don’t need to use the plugin on the production site. The plugin is to edit and export a fully working theme that you can use in your production site.
Let’s see a concrete example of a typical use case:
You are creating a theme for you or a client in you local computer using the WordPress site editor. When the theme is good to go, you export the theme using the plugin. After that, you upload that theme to your live production site and, that’s it. You have you theme working nicely in your live site.
