Thanks for the ping, Marius! I've been quite busy with some yak shaving tasks, but my importer is already working and has some interesting improvements, like elegant module fetching from the official module proxy, license extraction and recursive import support.
I need to fix an esoteric bug that trips the kernel's out-of-memory killer when building a derivation with dependencies, but the importer part works pretty well.
You can take a look to [my changes] for some readily backportable ideas, like [the compact algorithm for uppercase path escaping].
Please forgive the code quality and the possible backwards-compatibility mistakes; this is an unfinished proof of concept.
$ guix import go-modules -r github.com/FiloSottile/age
# Please refer to the issue 43872 for more information about the resting environment