Although we're technically in the beta part of the release cycle, we've still been spending some time on features for future releases. I've been working on adding a macro/scripting style environment to Mixxx which would allow users to extend Mixxx without the work of recompiling. Here's a screenshot of the very basic test GUI in action:
The script interpreting is done using the new QtScript ECMAScript interpreter built in to Qt 4.3 and the example you can see typed in above implements a basic auto-crossfader.
The potential here is fairly unlimited. API documentation and so on will follow soon so that people using Mixxx from SVN will be able to have a play.