SuSE Linux (around since the 90s) had such a single-layer-manages-everything approach, so yes, it’s not a new concept.
I used to think that you don’t need Nix to get most of the benefits that Nix/NixOS are known for. And to a certain extent, that’s true — you can achieve much in other scenarios. But by now, I think the reason why Nix/NixOS work well and deliver these powerful abstractions is because they are Nix all the way down, giving you an unparalleled level of integration/reach for your declarative layer.
I used to think that you don’t need Nix to get most of the benefits that Nix/NixOS are known for. And to a certain extent, that’s true — you can achieve much in other scenarios. But by now, I think the reason why Nix/NixOS work well and deliver these powerful abstractions is because they are Nix all the way down, giving you an unparalleled level of integration/reach for your declarative layer.