> Betting on JS "evolving" is the wrong way to go.
Why? It is evolving. Slowly, but it is evolving.
Enough to cast a doubt on the viability of Dart and Typescript.
I think Typescript is in a different boat. All valid JS is valid Typescript, and Typescript is adding new JS features faster than browsers can. If JS ever catches up to Typescript it'll be by becoming Typescript, basically.
The rate at which JS evolves has been determined quite rightly by browser market share and aut0-updatability. When your clients need to upgrade their VM when your language changes, the only way to ensure progress is to make sure all your clients are running latest auto-updating versions. This is beginning to happen now, which is why the V8 and the language itself can start to make real progress.
JavaScript proved squat. Those changes should have been done a long time ago and now we should have had a sane language instead of JS. Betting on JS "evolving" is the wrong way to go.