Something similar was done in the Left 4 Dead series with the AI Director:

Tim Larkin: We took several steps to keep the music interesting enough that the players would be inclined to keep it on as they play. We keep it changing so it won't become tedious; to this end, we created a music director that runs alongside the AI director, tracking the player's experience rather than their emotional state. We keep the music appropriate to each player's situation and highly personalized. The music engine in Left 4 Dead has a complete client-side, multi-track system per player that is completely unique to that player and can even be monitored by the spectators. Since some of the fun of Left 4 Dead is watching your friends when you're dead, we thought it was important to hear their personal soundtrack as well. This feature is unique to Left 4 Dead.

For single-player it works really well for building tension leading up to being attacked by waves of zombies and creating calm spots after high-stress encounters.

In the online versus mode however players got really good at using the musical hints as "tells" for when certain actions happen in the game. Most notably there were musical signatures consisting of a few notes that would play when the special infected characters spawn. Coordinated teams could use this to their advantage know when the infected team is about to stage an attack (like an ambush at a choke point in the map).

https://www.youtube.com/watch?v=vAYd8ihcUVA

That could be very interesting.

Every gameplay a different soundtrack. Sounds fun.

Even more interesting if it allows variations in the same soundtrack according to different dramatic moments in the same scenarios. Example: a man is walking down the street vs a man is walking alone in the night down the street vs a man is walking alone in the night down the street unaware of a bright red dot on his back. All these scenarios could use the same soundtrack, but require different dramatic levels. The game would send data to the music algorithms so that the soundtrack would reflect the right mood.

Contrast with this very human representation of writing gameplay musical scores. Including the simple chart used to show segued clips.

http://www.audiogang.org/chance-thomas-composer-of-dota-2s-2...

There have been covers of people taking a pre-recorded segment of a game (say, a 1v1 fight), and improvising a jazz score around it. How awesome would it be to have this happen live for any game? Anything from mood to specific sound effects.

Or take real-time input from Fitbit and generate a soundtrack for you in real life.

Brilliant idea.