I love the points made and this brings up a very good question.
This is partially put to the test in some games today, but I dont think it can be perfectly inserted. As stated, gaming is not a movie. You cannot create perfect chords and ballads to something that is always changing. You can set the mood with a certain song, but in my opinion I dont think it can be adopted.
I was thinking along the lines of adding more in depth music, something that when you here it, you remember those times killing the last terrorist and saving the world, but that can already be done.
How can we add music without breaking the concentration of the user?
The best music transitions Ive heard so far are probably in final fantasy or Halo, but its just setup so when the player reaches a certain point the new music kicks in.
"Most importantly: how can a game composer score a scene intelligently and compellingly, when she doesn’t know what is going to happen, when?"
I think the composers should work closesly with the level designers etc and just make sure they have the right music for the right parts. I love it when you get into a tight jam and there are alot of baddies waiting for my to peak my head out. The music plays such an important roll in the dramatic tension and creates more depth and mood for the player. It is impossible to know when the player is going to run or when the player is going to hide, all we can do is just set the scene the way we think it will effect the player the most, cross our fingers and hope for the best.