Well, I think he is completely right that bitcoin mining will become unsustainable unless some major change happens. The problem is that you need a huge hashrate to keep the network secure enough, but this hashrate costs a lot of money in terms of energy consumption. This has to be paid by someone.

PMC is of course already experimenting in this direction, but has a major problem imo, which is the hashrate. With a max of a few hundred GH/s, it is very easy to do a 51% attack. Someone with two or three ants could probably already do it (if he has the knowledgde how to do it).