When I used it (and I did use it enthusiastically for awhile) NixOS had other issues. Chiefly, large portions of real world configuration did not conform to its model. While you could in theory make anything work, I found that managing actual configuration (already enough of a challenge) with the additional backflips of straining it through the NixOS model was just not worth the time. It worked well for simple configurations that were well used, but once you strayed from that path it became increasingly tedious, while you also had the NixOS change risk added to everything else to manage over time. Final assessment at the time: relatively inappropriate for complex configuration requirements. Could be time for a revisit.