Hoo boy, `guix import npm` was not an easy task to put on a poor #gsoc. No shade on the developer, I think people simply underestimated the challenge. I would say they got enough done to be proud of their work.
I'm noting that node-build-system.scm is still absent from http://git.savannah.gnu.org/cgit/guix.git/tree/guix/build-system .
https://github.com/jellelicht/guix/pull/1
Nix has https://www.npmjs.com/package/node2nix , which is more focused on getting this thing done than doing it neatly. It does it surprisingly neatly given the circumstances. But it can't handle e.g. scuttlebutt-secure because of binary npm deps (the first one it croaks on is leveldown, which tries to get leveldb using prebuild-install).
For a taste of how difficult npm-ery is, I'll post a few links to http://sandervanderburg.blogspot.com/ .