> Typescript doesn't implement new Javascript features until their addition to Javascript itself is imminent.

I guess we want different things from Type systems.

I want rock solid guarantees that code is correct, so that the only thing left to test as much as possible is the business logic. I don't care about the latest programming fads, and I want stable, performant code.

You seem to just want some boilerplate guarantees and backwards compatibility.

If I were writing/creating TypeScript, I would be not implementing new features before JS upgrades, but long after (possibly as support libraries). I understand the goal of "easing" the transition, but IMO those sorts of "upgrades" should be late, not early, in a tool whose primary goal is static type checking, not JS features.