For more than a year now, I've been developing my own content management system called Tux CMS (http://blogwithtux.org), which takes a lot of its feature ideas and concepts from WordPress (I've also ported a few WP themes over to it). Extremely little borrowed code, but a lot of borrowed inspiration, so first of all, I'd like to say thanks to the WordPress team for an awesome product! :)
Second, though, I would like to suggest a feature. For the past few months I've been getting fed up with XML, and getting to know JSON. XML can be quite clunky, and really isn't suited for syndication when you think about it. JSON, on the other hand, is a very lightweight data serialization language, which greatly improves size and simplicity of use of syndicated content (it has direct relationships to programming structures, so it's easier to access programmatically than XML through the DOM).
I'm trying to get a movement going of a syndication format made completely in JSON. The first step, I figured, was to develop an informal specification: http://howto.blogwithtux.org/index.php?title=JSON_feed.
The next step was to create a working implementation of my specification: http://www.mattpat.net/json.php. But then, when trying to decide on the third step, I wondered, hmm, what would get this the most exposure? Why, implementation by one of the best and most widely used blogging engines, of course! I'm a big fan of WordPress (despite the fact that I write my own CMS... of course, it's open source, so I would call it more friendly competition), so I thought I might start here.
Is this something WordPress developers might be interested in? I want to make this a large movement... I even wrote an article on A List Apart for it (still waiting for a response on it).
Let me know!