With https://github.com/nlewo/nix2container, I'm trying to make a more standalone tool. Basically, a Go binary takes a reference graph and produces a JSON file describing a container image. This JSON file is then ingested by a Skopeo fork (it adds a new `transport`) to produce images (to file, registries,...).
Currently, it supports the dockerTools layering algorithm and is designed to work with Guix [1] as well;)
Ah, I've actually seen this before. Since it's written in Go, you might be able to pretty much copy&paste the Nixery layering strategy into it. I wouldn't mind!