Coming from no special knowledge in nuclear weapons, reading this had the impact of making me more scared from a nuclear arms race and from miniaturization of nuclear weapons. Also, I am more inclined to be feel threatened by improvements in fusion energy or subatomic physics.
I guess I was surprised by the aspect of improving nuclear capabilities, although it should have been obvious that countries are doing just that if I had given it some thought. A concrete example of this is also making it more tangible.
But it's all Okay! As evident from the closing remark by a nuclear physicist Lei Yuan: “But I don’t think we need to worry about this, not until we see a real new bomb. The technology is so difficult, it remains more fantasy than real threat.”