WP-Minions ( https://github.com/tott/WP-Minions/tree/alter-job-data ) for multisite syndication to one site.

minions-post-pusher.php

<?php
/**
 * Plugin Name: WP Minions Post Pusher
 * Description: Pushes all published posts to one blog using wp-minions
 * Version: 1.0
 * Author: Thorsten ott
 * Author URI: http://thorsten-ott.de/
 * License: GPLv2 or later
 */

if ( ! defined( 'WP_MINIONS_POST_PUSHER_TARGET' ) ) {
	// nothing to do for us
	return;
}

if ( defined( 'WP_IMPORTING' ) && WP_IMPORTING ) {
	// don't run during import
	return;
}



if ( get_current_blog_id() != WP_MINIONS_POST_PUSHER_TARGET ) {
	// if we're not on the main site then we hook into post transitions to run our async calls
	add_action( 'transition_post_status', 'post_pusher_handle_post', 1000, 3 );
}

function post_pusher_handle_post( $new_status, $old_status, $post ) {
	if ( 'publish' != $new_status && 'publish' != $old_status ) {
		// we only act on published posts
		return;
	}

	// inject our post data and blog id
	add_filter( 'wp_async_task_add_job_data', 'post_pusher_adjust_job_data', 10 );
	// schedule async tasks
	wp_async_task_add( 'post_pusher_add_post', array( 'new_status' => $new_status, 'old_status' => $old_status, 'post' => $post ) );
	// remove injections
	remove_filter( 'wp_async_task_add_job_data', 'post_pusher_adjust_job_data', 10 );

}

// manipulate job data before we send it to the queue, eg inject blog id
function post_pusher_adjust_job_data( $job_data ) {
	$job_data['args']['original_blog_id'] = $job_data['blog_id'];
	$job_data['args']['original_post_id'] = $job_data['args']['post']->ID;
	unset( $job_data['args']['post']->ID );
	unset( $job_data['args']['post']->guid );
	$job_data['args']['post']->post_name .= '-' . pusher_id2alpha( $job_data['blog_id'] ); // we do this to ensure post-name uniqueness
	$job_data['blog_id'] = WP_MINIONS_POST_PUSHER_TARGET;
	//error_log( var_export( $job_data, true ) );
	return $job_data;
}

// run our callback for the worker that creates / updates the posts
add_action( 'post_pusher_add_post', 'post_pusher_add_post_callback' );
function post_pusher_add_post_callback( $args ) {
	global $wpdb;
	//error_log( 'Executing post callback' . var_export( $args, true ) );
	// $args = array( 'new_status' => $new_status, 'old_status' => $old_status, 'post' => $post )
	if ( ! isset( $args['post'] ) || ! isset( $args['new_status'] ) || ! isset( $args['old_status'] ) ) {
		return 'Missing data ' . var_export( $args, true );
	}

	$update = false;
	$post = $args['post'];
	$post = (array) $post;

	// currently just checking for the post name, might be more elegant to check for original_*_id postmeta
	$check_sql = "SELECT ID FROM $wpdb->posts WHERE post_name = %s LIMIT 1";
	$post_ID = $wpdb->get_var( $wpdb->prepare( $check_sql, $post['post_name'] ) );

	if ( ! is_wp_error( $post_ID ) ) {
		// re-inject post_id to force post updates if a post exists
		$post['ID'] = (int) $post_ID;
		if ( $args['blog_id'] != get_post_meta( $post_ID, 'original_blog_id', true ) || $args['post_id'] != get_post_meta( $post_ID, 'original_post_id', true ) ) {
			error_log( 'Invalid post push : ' . var_export( $args, true ) );
			return false;
		}
		$update = true;
	}
	// insert / update post
	$post_id = wp_insert_post( $post );

	// inject post meta to store reference to source
	if ( $post_id && false === $update ) {
		update_post_meta( $post_id, 'original_blog_id', $args['blog_id'] );
		update_post_meta( $post_id, 'original_post_id', $args['post_id'] );
	}

}



function pusher_id2alpha( $id ) {
	$dictionary = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
	$dictionary = str_split( $dictionary );
	if ( 0 == $id ) {
	    return $dictionary[0];
	}
	$result = [];
	$base = count( $dictionary );

	while ( $id > 0 ) {
		$result[] = $dictionary[ ($id % $base) ];
		$id = floor( $id / $base );
	}

	$result = array_reverse( $result );
	$string = implode( '', $result );
	return str_pad( $string, 4, '0', STR_PAD_LEFT );
}