What if flake outputs were a module?

flake-module.nix

# specialArgs provided as module parameters:
# - pkgs = inputs.nixpkgs.legacyPackages.${system};
# - inputs = flake.inputs with ${system} stripped
# This design requires two phases:
# 1. First evaluation collects all `meta.platforms`. While doing this, we set `pkgs = {};` and `inputs == {}`.
# 2. Than we evaluate for every output attribute and for every platform listed in `meta.platforms`.
# TODO: How to make outputs extensible?
# Do we even want this? Maybe having a standard interface would be better?
{ config, pkgs, inputs, ... }: {
  meta.platforms = [ "x86_64-linux" ]; # defaults to nixpkgs.lib.defaultPlatforms;

  checks = {
    meta.platforms = [ "x86_64-linux" ]; # defaults to config.meta.platforms;
    meta.default = config.checks.hello;
    hello = pkgs.hello;
  };

  apps = {
    meta.platforms = [ "x86_64-linux" ]; # defaults to config.meta.platforms;
    meta.default = config.apps.hello;
    hello = {
      type = "app"; # defaults to "app"
      program = "${pkgs.hello}/bin/hello";
    };
  };

  packages = {
    meta.platforms = [ "x86_64-linux" ]; # defaults to config.meta.platforms;
    meta.default = config.packages.hello;
    hello = pkgs.hello;
  };

  devShell = pkgs.mkShell {
    meta.platforms = [ "x86_64-linux" ]; # defaults to config.meta.platforms;
    buildInputs = [ pkgs.hello ];
  };

  overlays = {
    meta.default = config.overlays.default;

    foo = {};
  };

  templates = {
    meta.default = config.templates.hello;
    hello = {
      path = "<store-path>";
      description = "template description goes here?";
    };
  };

  nixosModule = {
    meta.default = config.modules.hello;
    hello = { ... }: {
      imports = [
        inputs.input.modules
      ];
    };
  };

  nixosConfiguration = {
    hello = inputs.nixpkgs.lib.nixosSystem {
      system = "foo";
      modules = [
        config.modules.fancy-module
        ./configuration.nix
      ];
    };
  };

  hydraJob = {
    helloHydra = {
      hello = config.packages.hello;
    };
  };
}

flake.nix

{
  # ...
  outputs = flake-modules.lib.outputs {
    imports = [
      ./flake-module.nix
    ];
  };
}