Coffeescript was a good thing when we only had ES5. In fact many of the things it championed made it into ES6 and beyond. I think with TypeScript it isn't just a shiny thing. If it does substantially change I believe it will be to break the forced compat with JS. As WebAssembly gets more adopted it will be possible to not have JS targets, and thus remove a lot of the weird JS things that have been kept for compatibility. Typescript has the gravity to continue.