After running NixOS for 6+ months on my homelab and also re-using part of the configuration on my work machine, I feel the same way as Xe each time I'm interacting with a non-declarative OS. There's just no simple way to share configuration between machines or to automagically clean things up after making changes.

Ansible feels like a thin layer of ice upon a deep ocean of the OS state, hiding in a multitude of non-tracked configuration files. It is simply not enough to build a layer of YAML around an OS which is imperative by nature.

Unfortunately, I can see the downsides of NixOS as well, being radically different from what we usually expect in a Linux distribution, adopting it in a already established environment will no doubt be hard. Steep learning curve, idiosyncracies of the Nix language (although after reading parts of the Nix thesis[1], I find it much more understandable and deeply thought out), just explaining Nix to people who don't have much experience with the functional way of doing things, let alone taking the functional approach all the way to defining an entire operating system - all of this sounds like a tough barrier to cross.

And yet, the desire to keep things reproducible and declarative (not to mention going back in time) persists once you've had the taste of NixOS.

[1] https://edolstra.github.io/pubs/phd-thesis.pdf