Nitpick: binfmt.emulatedSystems is not true cross compilation. It sets up a nixos to enable emulated native compilation. After painful tinkering, i prefer this way too. When i recall correctly, for cross compilation you'd have to use nixpkgs flags.
At some point it's a matter of perspective. If the emulated system is fast, it feels the same as "true" cross compilation. In the end it's a bunch of bits and bytes which produces some other bits and bytes when we poke it. If it goes fast, it's good. If it goes slow, it's painful.
