Fascinating, should have blogged this sooner. I truly hope that when Atom finally gets standardized and released that this kind of innovation will occur. Bring it on!
What Atom says is: If you want to afford these behaviours, then you have to be weblog-like in this respect and editor-like in this respect, and it doesn't matter what else you do, but those are the shapes we require.
And because Atom demands this certain minimum set of data, which has been decided by experience and thought, you can use [will be able to use] any editor, any weblog system that accepts posts, any templating system. What I'm describing here is the loosely coupled architecture, and what the benefit is, is evolvability.
We've had a lack of innovation in the weblog space because there aren't decent abstraction layers. You can inject posts, that's it, but bound together are: the datastore, templating, display, editing, permissions, commenting and so on. Occassionally there's some innovation -- there was a website that sold Blogger templates for a while, I believe, and MovableType plugins extend the templating and display systems wonderfully. But the applications themselves are still monolithic.
Atom says: Given everything else is in flux, here's our one fixed point. The post. The metadata of the post. The relationships between posts. That's it.
Out of that single abstraction everything else can crystalise.