I remember reading about your project a previous time NixOS had been mentioned on HN, and tried to look for it again but couldn't manage to bring up the correct set of keywords to find it.
Thank you for posting it again. I don't think I'll go back to Arch unless I grow tired of NixOS, but if I do I'll be sure to give it a spin!
Here is my attempt at solving this problem: https://github.com/CyberShadow/aconfmgr