This could be even easier to implement than the author suggests, at least for the cited use case of when a new web page is published (e.g. Part 2 of an article). The simplest solution--assuming you know what the URL will be--is to have your agent of choice periodically check whether that URL returns 200. That greatly simplifies the protocol since it piggy-backs off the existing HTTP protocol, and makes it easy to write your agent (or use an existing one). All that's left would be for authors to publish what the next URL will be; nothing else on the back end is needed.