From what I can check internally, this has been replaced by A default site template[1] that is available out-of-the-box and that defines a theme for the Core Components and a set of corresponding templates that can be used to generate a new site from the Create Site Wizard. This default site template will also serve as a reference for further more use-case-specific site templates that web agencies can create with the Simplified Frontend Workflow.
[1] https://github.com/adobe/aem-site-template-basic