Yes, very nice stuff! I recently used nixos-generators to create an lxc image that starts up, performs a task, and shuts down again.
The image is intended to be deployed on a non-NixOS server later, but testing it locally on my NixOS machine with lxd was pretty straightforward.
Overall I found the experience very nice. Great how only the ‘run-time closure’ of the system as calculated by Nix needs to be included in the image. The default configuration is still a bit overkill (mostly systemd), but I didn’t see to override bootStage2 with something leaner (Replacing the bootStage2). Anyway it’s not too bad as it is .