> Plus, it gives (or will give) much lower-level access to features like threads and memory allocation.

There's no reason JavaScript couldn't just have those features. It already has some amount of memory allocation control via ArrayBuffer & DataView.

Thanks to Spectre I don't think we'll be seeing threads anytime soon. Well, not threads with shared memory anyway which removes a lot of the point of them. Same reason JavaScript just lost SharedArrayBuffer, too easy to make a high precision timer out of it.