Here’s something interesting:
RSS Ping combines RSS item metadata with site update information. It enhances the current ping specification, adding information about exactly what has been updated or published, with the notification that something has been updated. RSS Ping reduces the need to revisit or work done by aggregators and search engines when revisiting the publisher site after being pinged, to provide truly real-time updates for information on the Web.
For what I can make of it, it’s meant to extend the current ping standard by letting the ping server collect a so-called ‘payload’. The payload is nothing more than a feed with a single item. Therefore eliminating the need to collect the originating page or complete feed.