Hacker,
I was thinking af a similar idea earlier today. That would go really nicely if MC could set up a way to allow real-time beat-matching. It can analyze the end of the currently playing track for its' beat, and sync the next track to match that beat and crossfade into the new track. It would make for nearly seamless playlists automatically.
In addition to having MC pick songs based on your rotation categories (Heavy, Medium, Light), it could also vary the intensity or bpm in the same semi random fashion, to really mix up the mood a little. 4-5 songs of upbeat techno, 1-2 songs of downbeat, a little funk, trance, upbeat again, etc.
Then engine to drive these 2 similar ideas could be the same, the variables would just have to be changed. i.e. how frequent of a change, how long the change should last, how many criteria to include in the mix, etc. We just plug in the variables.
Jim, do you think you guys could do something like this? I know a lot of DJs would really be able to use this kind of thing.