We (as far as I can tell) use some parts of systemd-networkd by default (as in, even if you haven't enabled it), as MAC addresses via `networking.interfaces.<name>.macAddress` are set through it: https://github.com/NixOS/nixpkgs/blob/65e07f20cf04f5db9921dc...

kstenerud: I assume you tried that option?

Edit: ah, you caught that in an edit :-)