[kakwa_]

In the end, Nix is just a thin veneer on this stuff.

Given how many quick & dirty sed patching or exec commands I've seen in the few nix package/modules I've read, I would not exactly bet my life on it being completely idempotent & reproducible.

[kkfx]

it's the best option after IllumOS (OpenSolaris) IPS integrated with ZFS. Far less powerful not imposing zfs (only well supported for root, swap, encryption etc), so not integrated in the package system and bootloader management (BEs, Boot Environments).

It's not reproducible bit by bit, it fetch the current version of anything, but it's still easy to reproduce enough, stable enough and complete enough, while classic distros need a fresh install every major release or facing issues an keeping a system in unknown state for long until it explode.