Comment 1 for bug 1131460

This would leverage the fact that Mixxx has already implemented a fairly robust MIDI scripting system - most software (at least on Linux) doesn't have any scripting functionality built-in - you might be able to map controls, but there's generally no ability to do anything more complex than a direct mapping.

Conceivably, complex functionality could be scripted in something like Mididings, and then routed to Mixxx as well as to other software, but then Mixxx wouldn't benefit from mappings that could be easily shared with the community. By providing MIDI outputs, mixxx might be able to attract more users and script developers by allowing the scripting interface that's already been created to be used as a relatively accessible programmable midi router.

...and, in case it's not clear from my initial post, in addition to simply passing through signals from a physical controller, mixxx scripts could generate their own midi messages, possibly based on characteristics of the song that's currently playing - triggers could be sent to external samplers or effects based on song tempo, etc...