Wat?
Latency (how long it takes for messages to travel back and forth), which is where X11 over the network has major issue, doesn't matter in the specific case of watching a video.
Essentially, once you press 'play', there's just a torrent of data flowing down from the server to the client with very little need for two-way banter between the machines.
It's not even fair to compare it to waypipe's h264 compressed buffer feeds.