The Docker Registry V2 API has a
_catalog endpoint responsible for listing image repositories. For most private registries it makes sense to list all image repositories since it would be relatively few, but obviously for GitHub it is not OK to list all image repositories.
That said, it would be possible and IMO practical to list all image repositories for repos the user has package push access to–essentially, those for which they are responsible.
Some flavor of the above functionality for the
_catalog endpoint is needed for the VSCode Docker extension to show GitHub as a package registry in the explorer view.