Linking a nixosConfiguration to a given homeConfiguration

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2

Why not use home-manager module within nixosConfiguration? Something like below:

nixosConfigurations = {
        hostName = nixpkgs.lib.nixosSystem {
          system = "x86_64-linux";
          modules = [    
            ./configuration.nix
            
            home-manager.nixosModules.home-manager
            {
              home-manager.useGlobalPkgs = true;
              home-manager.useUserPackages = true;
              home-manager.users = {
                user = import ./home.nix;
                root = import ./root-home.nix;
              };
            }

          ];
        };