It seems to me like natural behavior that, by default, git pkgs diff outputs a diff for the dependency changes that have not yet been committed. Unlike git diff, which outputs the diff of unstaged (or staged with --staged), right now the output for git pkgs diff is for the last commit instead.

I would like to use this, for example, after I run npm update (or similar for other ecosystems) because there can be loads of changes that are otherwise hard to review.

This might be hard to implement as I did not figure out a way to achieve this use the --from and --to options and git diff might be leveraging some non-trivial plumbing (or worse, internal APIs) to display the diff of the staging area...