It seem to me the Editable Templates are useful for a single site usage as design/policies configurations are defined on template level. i.e. imagine to identical sites in structure but they have different design/policies configurations for structural components (ex. header, footer), then in this case you will need to create to set of identical editable templates to be able to define different policies for the structural components on those sites, which does not seem like a beautiful solution to me. Are there any other ways for defining different policies for structural components per site on the same editable template?

In static templates world the design configuration are fetched from the designpath which is configurable per site, but this is not the case here, unless it is possible to define policies per site,

conf->project->settings->wcm->templates

                                                             ->[templateA]
                                                                       ->policies
                                                                                  ->[siteA]->header
                                                                                 ->[siteB|->header