[stevvooe]

Note that I did not say "more granular layers" but more "more granular filesystem representation". This is a key point in achieving better data sharing. In fact, these use cases are not ruled out, but bolstered by OCIs approach. The introduction of alternative systems will be much easier to do when OCI is broadly implemented.

As far as metadata is concerned, your suggestion is exactly what OCI does. The problem with ACI is that it embeds a large part of the metadata into a tar file, which has to be fetched in its entirety. OCI is mostly metadata scaffolding, made up of indexes, manifests and configs that can all be fetched without large bandwidth requirements.

The compositional aspect that you've brought up has been explored and it doesn't make a whole lot of sense to cram that into images. Typically, such a system requires composing container filesystems through named references, allowing components to be independently rebuilt. Because this composition often relies on details of the target deployment media (orchestration system, container runtime, specific operating system, etc.), especially in how it deals with the security of name resolution, baking it into an image format leads to massive inflexibility.

Moving it up the stack works much better and avoid the technical complexities that come with doing it within images. We can see this image composition in action in k8s PODs, docker stacks and other systems. Such constructions can be distributed through OCI images, through media types, but they are based on the compositional capabilities of the target system.