The TypeScript team has a goal of keeping it a superset of JavaScript. This means that when JavaScript gets some new features, TypeScript also supports that. If TypeScript supported it before with some other syntax, the syntax gets changed. [1]
The hero feature of TypeScript, static typing, will never be available in pure JavaScript based on any current prophecies.
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[1] One reason the object spread/rest situation took so long was because they didn't want to implement it and then have to change the syntax/meaning later. It's better to wait until new proposals have gotten a decent amount of progress, so that they're fairly stable. Do note that spread/rest still isn't in the JavaScript standard, it's a proposal.
Side related question- has this going outside of standards with such things as Typescript been harmful? I mean, standards move slowly, but your question raises an interesting point - why didn't we just extend actual Javascript to have typing supported? Have we given up on advancing the core language in such regards?
ES4 attempted to add type support. (It's the ES version time forgot, mostly known only for forks it spawned like Adobe's ActionScript.)
Typescript and Flow both resemble, to different degrees, the type support that ES4 attempted (pascal-style `: typename` annotations being common to all of them).
Presumably the reasons browsers were not interested in ES4 remain the case today.
If that changes, then Typescript/Flow are useful playgrounds to explore what the standard could be. Many ES proposals now require "prollyfills" exploring that feature in the space of existing browsers as proof-of-concept, to help explore possible complications. Typescript and Flow do good jobs of "prollyfilling" type support, and I would expect that if a new attempt to standardize types in ES were to occur, they would both be looked to for advice/guidance.
The hero feature of TypeScript, static typing, will never be available in pure JavaScript based on any current prophecies.
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[1] One reason the object spread/rest situation took so long was because they didn't want to implement it and then have to change the syntax/meaning later. It's better to wait until new proposals have gotten a decent amount of progress, so that they're fairly stable. Do note that spread/rest still isn't in the JavaScript standard, it's a proposal.