Matt Webb perfectly articulates my attraction to Atom:
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.
The crystallization of which Matt speaks is, of course, the most promising reason to use Atom. I've only met two kinds of people: 1) those who think the most important thing is to formalize all data, aggregate it, distribute it, and then go crazy doing interesting things with it, and 2) those who find me boring at parties (since this is the type of thing -- often, unfortunately -- I like to talk about at parties).
A key feature of future blogging tools, as Matt sees it:
A templating system. Probably a cgi script that does XML transforms (so I can trade templates with people, because we all know we're operating on collections of Atom documents), or a Movable Type-like templating tool.
Some of this site's templates are already XSL-Transformations acting on Atom documents. They'll all be standard XSLT, eventually -- when I find a Perl module that supports everything I want do do with XSLT, I guess -- and they'll all be operating on Atom. At which point I'll make them available to the rejoicing masses, who'll bask in the new interwebtopia. And you'll say, "Look! I wrote an Atom transformation, too, and look how it does all these interesting things." And I'll think you're very clever and be inspired to do my own interesting things.
That's how it looks in my head, anyway.
Fundamentally, this is not a new idea, but Atom actually makes it seem possible.