No. Nix requires much less maintenance than gentoo. The maintenance it does require is typically very fast. Gentoo builds everything from source and portage is not immutable the way Nix is. My experience running Gentoo (and I ran it during the GCC 3 -> 4 upgrade, which required a full emerge world) is that updates cane be slow, and prone to breakage, due to missing or clashing or outdated dependencies.
Nix is a dream come true. Due to the way the nix store keeps all dependencies separate and reproduces builds to a high fidelity, when you do need to build a system package (very rare, as most are just downloaded straight out of a binary cache), it will invariably succeed with few exceptions, and the resulting binaries will work correctly.
But the best part about nix vs portage is that it won't leave your system in a half way state. Upgrading NixOS means downloading or building a bunch of packages. This can be interrupted at anytime. At no point during the download or build will the old system become unusable. Nothing in the old system is overwritten. At the time you have everything built and are ready to change, the change occurs atomically and instantly. If the new system does not work, you can revert back to the old system atomically and instantly as well. In the rare case that the new system has made your computer unstable, you can reboot the system back into the old version without the need for a rescue CD or USB stick.
OTOH, if you're like me, and want to update to get a new version of one package (and its dependency tree), it's a very common experience to find out that some completely unrelated option has changed in some backwards compatibility breaking way such that I never had to deal with when I ran Arch Linux.
You can use nix-env -i of course, but then you have a duplicate package (that can be out of sync and easy to forget about) and this doesn't work for anything with a systemd service.
I like that I can't really fuck up my NixOS installation, but I actively dread updating (although it's got a lot better in the last year). I'd love a NixOS alternative that took backwards compatibility a lot more seriously.
One of strengths and at the same weaknesses of Nix is that it is not very opinionated. That means there are many ways of doing the same thing. I'm wondering how were you backporting a new package.
For example pgbouncer version that was used was a bit older than I wanted, I was easily able to update the derivation and also enable c-ares name resolution by overriding the derivation like this:
I'm not even talking about backporting, rather updating to the latest version in NixOS unstable means running nixos-rebuild switch --upgrade... And this often seems to fail due to non-backwards compatible changes. Sure, it happens more on unstable, but the software in stable is often too far out of date or worse, broken (e.g. by the download link expiring).
Updating the package is typically a means to an end—this month I had to upgrade emacs due to a melpa package update, and python due to a work script requiring 3.7.3—the last thing I want to be doing is maintaining my general system. Even writing an override feels a bit ridiculous (it's right there in the channel!).
What I inevitably end up updating my nix-env channels and using nix-env -i to install the new package. This works most of the time, but the insidious thing is that I usually forget that I even have this dynamically installed package, and never update it. That is, until it breaks my system in some subtle way.
So yeah, if something came out with all the benefits of NixOS (and I love the nix package manager, the safety it provides, and the pure functional declaration of all the dependency trees), but with the respect for not breaking backwards compatibility that you see in functional programming communities like Clojure, then I would be in love.
+1. It's been years since I used Gentoo, but I felt like it broke me, or required some sort of intervention once a month. Arch was much better, more like once every few months. So far Nix has not broken anything for me in a year of use.
