The 404s are to the author’s own GitHub repo and are not a reflection on Nix. It looks like they deleted and recreated the repo with the name wagdav.github.com and just didn’t update the links in this post accordingly.
But it is reflective. I've found that sort of thing rampant in it's community, and sometimes it's own docs. It doesn't mean it's bad tech, but will be hard to convince a corporate group to want to use it.