The author mentions WebAssembly, yet writes at the end : " and a security model that allows us to forget that we run thousands and thousands of untrusted scripts every day." WebAssembly is designed to run in a sandbox. I suppose that does not by itself make it completely safe, but it can not be much worse than the current situation, can it?
What many people think it is: I can compile my JS frameworks as assembly and ship binaries to the browser, that'll run near-native and be more compact.
What WebAssembly actually is: a way to compile libraries from other languages in a manner that you can run them in a JS runtime, but with no access to the DOM, etc. (Think of things like shipping a JS based OCR library or a JS based audio-engine that runs at near-native speeds)