> This feels like the beginning of TypeScript throwing its weight around. It has the momentum to supplant JS and this is an exploratory compatibility-breaking step.

If this dream will come true, we will have both broken JS development space, and not much better TS developer ecosystem.

The creation of TypeScript is Microsoft's doing its trick called "Extend Embrace Extinguish."

They see that their captive developer community of VB and C# devs is trying to migrating to more sane scripting languages, and they want to cauterise the bleeding with TS.

The moment TS will gain steam, they will very likely add some extensions that will finally break any form of reverse compatibility, and make TS a standalone language. And few years down the line they will put a lid on it too.