So that means that it needs the host to run nix, right? I suppose that could be useful, but if I'm running nix-built images as containers it's usually because I want to run somewhere that's not "nix native".
That's fair, adding another service is definitely a downside. If you are running nix-built images though, the underlying data still needs to land somewhere on disk. Nix-snapshotter lets you store less data and download less data due to its package granularity.
We already have rootless containerd and nix-snapshotter. And I believe there is work underway to run rootless nix (and rootless k3s too). You may be able to run the whole thing unprivileged one day.
Even at the cost of the k8s nodes having to be "special", this is still fabulously useful running Nix-native workloads on stuff like GitLab or Jenkins workers.
We already have rootless containerd and nix-snapshotter. And I believe there is work underway to run rootless nix (and rootless k3s too). You may be able to run the whole thing unprivileged one day.