The big question here is who defines the events. I mean, the protocol suggests that the sender should describe the event and offer a simple button for it.

But in reality, the receiver knows a lot more about what he is interested in. Some people might want to get an update for the next blog post, while others may be interested in updates for the next blog post that completes a particular series, and so on.

When the sender defines the events, you can use a new protocol; however, if the receiver determines the events, all you need is a client with a rules engine (e.g., IFTTT).