It would be good if wordpress had the ability to render it's content as pure XML. Not just as part of some sort of import/export or an RSS capability, but as an option for browsing the content. Also provide a convention for apply XSL so that people can create themes using XML/XSLT without having to program in PHP code.
Rather than waiting around, I'm building what should at least be a proof of concept at some point, although it would do well as core functionality (as opposed to being implemented as a theme - to the exclusion of a normal theme). There is a blog at http://WP-XML.com - see the about page for a more in-depth discussion on the rationale (separation of concerns etc).