Could this be used without nix?

[VanCoding]

Hi & thanks for creating this interesting software

After looking at the code a bit I started wondering: Could this also be used without nix?

For example, if I have some binaries on disk and I'd want to put those into a bare docker image?

Also, what I am really interested in is the following scenario:

In a nix-shell, build some files
then build a container image that contains another nix shell with just the runtime dependencies, without any build tools and then add a layer on top that contains the built files from the previous step.

Is something like this possible, or is nix2container exclusively for fully nix-packaged software?