Formatter
It would be nice to have a basic formatter which manages indentation.
EDIT: Some reference: https://nixos.org/manual/nixpkgs/stable/#sec-syntax
In the meantime, hooking up nixfmt with a File Watcher works reasonably well:

Coming soon with the next release, there will be a new option in the settings which can be used to integrate nixpkgs-fmt and potentially other formatters. Thanks goes to @Cottand.
I think it would still be nice to have a very basic built-in formatter, which can at least handle the indentation in lists, attribute sets and let expressions. I will therefore keep this ticket open.
Can confirm this feature works, personally using nixfmt-rfc-style with the following command: nix --extra-experimental-features "nix-command flakes" run nixpkgs#nixfmt-rfc-style -- -w 240