default value for read only in submodule

default.nix

(import <nixpkgs/lib>).evalModules {
  modules = [
    ({
      lib,
      config,
      ...
    }: let
      niceSubmodule = lib.types.submodule ({config, ...}: {
        options = {
          text =
            (lib.mkOption {
              type = lib.types.str;
              readOnly = true;
            })
            // (
              if (builtins.any (submodule: submodule ? config.text) config._module.args.moduleType.getSubModules)
              then {}
              else {
                default = "readonly default value";
              }
            );
        };
      });
    in {
      options = {
        original1 = lib.mkOption {type = niceSubmodule;};
        copy1 = lib.mkOption {type = niceSubmodule;};
        original2 = lib.mkOption {type = niceSubmodule;};
        copy2 = lib.mkOption {type = niceSubmodule;};
      };
      config = {
        original1 = {text = "orig";};
        copy1 = config.original1;
        original2 = {};
        copy2 = config.original2;
      };
    })
  ];
}

start.sh

nix eval -f ./default.nix config