I don't have a strong opinion on this, but have the question: is the canonical-according-to-Nix name the attribute name, or is it the string in the option? I would say attribute name, which makes the current behavior correct.

Perhaps attr-name or just _ would be better, not sure.
Edit: Instead of nix-name

I believe it's the string name, which by default is the same as the attribute name [1] so it doesn't matter in most circumstances, except I have a weird setup where on my work machine my username has a different name to my home setup, so here the attribute name is default-user, and I use config.users.users.default-user.name and config.users.users.default-user.home in bits of the config

[1]

I marked this as draft because I noticed

Use of uninitialized value in numeric comparison (<=>) at /nix/store/w5s7s1nnzsmzdqh06abysffrj2m0nrwf-update-users-groups.pl line 253.
Use of uninitialized value in numeric comparison (<=>) at /nix/store/w5s7s1nnzsmzdqh06abysffrj2m0nrwf-update-users-groups.pl line 253.
Use of uninitialized value in numeric comparison (<=>) at /nix/store/w5s7s1nnzsmzdqh06abysffrj2m0nrwf-update-users-groups.pl line 253.
Use of uninitialized value in numeric comparison (<=>) at /nix/store/w5s7s1nnzsmzdqh06abysffrj2m0nrwf-update-users-groups.pl line 253.
Use of uninitialized value in numeric comparison (<=>) at /nix/store/w5s7s1nnzsmzdqh06abysffrj2m0nrwf-update-users-groups.pl line 253.
Use of uninitialized value in numeric comparison (<=>) at /nix/store/w5s7s1nnzsmzdqh06abysffrj2m0nrwf-update-users-groups.pl line 253.
Use of uninitialized value in numeric comparison (<=>) at /nix/store/w5s7s1nnzsmzdqh06abysffrj2m0nrwf-update-users-groups.pl line 253.
Use of uninitialized value in join or string at /nix/store/w5s7s1nnzsmzdqh06abysffrj2m0nrwf-update-users-groups.pl line 252.

in my PC's update, which is on 0f5ce2f, I'll see if updating it changes anything.

Hmm, fixed that problem, turns out it was my /etc/passwd containing

\0\0...\0::::::

that is, a lot of null characters, followed by an empty entry. Must have been some corruption at some point, that I caused, which would explain why I didn't see it on any other machine.

As above, the users.users.<name>.name is set on https://github.com/NixOS/nixpkgs/blob/c0fed202c43ae1091f0d0d8ec9678bdbabde02e6/nixos/modules/config/users-groups.nix#L282-L286

and for users.groups.<name>.name similarly
https://github.com/NixOS/nixpkgs/blob/c0fed202c43ae1091f0d0d8ec9678bdbabde02e6/nixos/modules/config/users-groups.nix#L338-L340

The users.users.<name>.name is already used in these places:

• For the home directory (this is just a bit below where users.users.<name>.name default is set).
  https://github.com/NixOS/nixpkgs/blob/c0fed202c43ae1091f0d0d8ec9678bdbabde02e6/nixos/modules/config/users-groups.nix#L287-L293

• In subuidFile and subgidFile, the attrValues are passed as user to the mkSub[gu]idEntry, and then it uses user.name (and only the .name from users). (If it were consistent prior to this commit, it would have used attrNames.)
  https://github.com/NixOS/nixpkgs/blob/c0fed202c43ae1091f0d0d8ec9678bdbabde02e6/nixos/modules/config/users-groups.nix#L378-L388

• In here, both for the inherit, and in the groups.members.
  https://github.com/NixOS/nixpkgs/blob/c0fed202c43ae1091f0d0d8ec9678bdbabde02e6/nixos/modules/config/users-groups.nix#L403-L418

Ah, I see #110627 implemented some of the changes from here (and closed #107353), perhaps it's worth looking over the remaining changes? I have updated this branch

@4z3