Dare: suppose the message exchange pattern is this: people who are registered can subscribe to my blog and I will POST updates via HTTP to the location of their choice?
They can treat this as a ping. They can aggregate it. They can route it to their in box. They can archive it. They can validate it.
Or perhaps I should also support SMTP. That's easy to do.
As you point out, I should probably also accept datagrams using the same format and interpret them as pingbacks or trackbacks or comments or...
I like the idea, and have no religion yet about the RDF debate that happens in his comment page.