Chris actually talked about it in a Q&A. He said: "No one's ever mixed music in this way and no one ever will again. So on the Pro Tools we track laid like every single sound in the music is track laid through the entire film, so rather than cutting the tracks they're all volume graphed because the automation and shift's done."
It's really fascinating.
I'd love to hear that 100 minute demo Hans did and I think releasing the score as a single 106 minute track would've been really interesting.
Christopher Nolan constantly touts how he aimed to have the soundtrack be completely non-sentimental, meanwhile he constantly uses Nimrod throughout the movie because his father was moved by it at a funeral. He tries to have his cake and eat it too. I don't think the results are particularly good. Variation 15 juxtaposed with Supermarine doesn't work very well. Variation 15 itself is nowhere as good as Time or other tracks that attempt to evoke the same feeling.