Really cool video. Music theory was 35 years ago, and I hated it so much I haven't played the piano since, but he did a fine job of explaining it all. I could never do what he does, but I can at least follow along as he does it.
Here's what jumped out at me, though: Does anybody still consider I&W their signature sound? Seems to me they never really sounded like that again, and have been steadily moving away from it with each album. Even ADToE, which many people think is essentially a reconstructed I&W (like he just demonstrated) doesn't really sound much like it, either tonally or stylistically.