Although note (didn't think to say this last night) that the video is no way contradictory to the idea of a security budget, or the consequences that fall out from reduced block reward. It is, instead, a graphical representation of how to visualize the dynamics of it -- in this case, it would move one of the curves to the right, as he describes; less existing mining capacity becomes profitable, and the area that can be mustered for an attack (those rectangles he draws) gets bigger.

Nothing really new there, unless I missed something. Just a formalization of game theory dynamics, which has been discussed many times by many people. Still, a nice visualization, and I always get excited when smart and thoughtful people explain things precisely, vs the usual suspects.