I recently developed a MediaWiki extension, that allows to export news in RSS 2.0 and Atom 1.0 format in easy manner. The extension is called "News Channel" and is now available at
http://www.mediawiki.org/wiki/Extension:News_Channel. Basically, when user or aggregation program requests a feed, the extension gets specified number of latest articles from some specified category (e.g. [[Category:Published]]), exports it to RSS/Atom feed format and sends to user. Articles's title will be the headline and article's text will be the description of news item. Feed is automatically linked from every page of the wiki, like recent changes feed is linked. First I developed it for my own site, but I thought it could be useful for other projects, especially for Wikinews. Customization is possible.