Having arbitrarily many segments is an improvement. In particular, we have some tooling that depends on a calculated image name, and we have to pre-pull and rename images locally if we store those in GitLab's registry.
I think for an Enterprise customer being able to push images that don't match the user/org pattern would be good too. While you couldn't allow just anyone to push e.g. 'ghcr.io/docker/docker:stable', I think this is a valid want for an internal/self-managed registry.
Our only namespacing enforcement is that packages must be published under a user or organization namespace for which you have write permissions. For example, I'd be able to publish under `ghcr.io/taywrobel/redis`, or under `ghcr.io/github/redis`, but would be disallowed from publishing as `ghcr.io/saxonww/redis`.
Other than that restriction, you can have nested image namespaces with arbitrarily many segments; i.e. `ghcr.io/taywrobel/dev/redis` would be valid.