You know, I don't see why Arch and other distros couldn't have a declarative abstraction layer. You don't hsve to go full Nix or GUIX just to hsve that.
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.
As far as "declarative abstraction layers" go, I think the reason that distros don't have them is because they exist one level of abstraction higher in tools like Ansible or Chef.
And thank god for that. I'm very thoroughly over declarative management systems: the world isn't declarative, and all these systems are only as good as their implementation.
Ansible at least doesn't lie to you about this: it provides the tools to be declarative, but doesn't pretend to understand your problems better then you.
Opinions differ, I guess. Ansible can't declare a desired state of anything at all and apply it, so I don't see much of a point in it over shell-scripts-over-ssh, other than maybe making decisions based on its fact gathering (but at the cost of having to deal with the yaml boilerplate).
Agreed Ansible isn't fully declarative like some other tools, but the variable management, roles, template engine, and integrated vault, are a big improvement from shell-scripts-over-ssh. Also in some cases, having yaml structure can be a good thing. Handing a pile of shell spaghetti to a new hire and expecting them to reason about it is less than ideal.
On Arch if I'm not mistaken, you can export your archinstall configuration to be used at other machines although it's not fully "declarative" but I believe it sort of works for certain use cases
