Using wp-cli, it is possible to generate random comments for posts. Is it also possible to generate sub-comments? If so; how?
Currently it is not available in WP CLI. See https://github.com/wp-cli/wp-cli/blob/master/php/commands/comment.php#L136
If you want, you can have your own customized comment generation command. See command cookbook. http://wp-cli.org/docs/commands-cookbook/