If this happened then JavaScript would be split into 20+ languages, one for each popular compiler. There would be nothing stopping a tool maker from adding their favorite language features even if no other compiler ever adopted them. That would be a disaster.
In many ways this has already started happening. TS has enums, Svelte has runes, React has jsx. None of these features exist in JS, they are all compile-time syntax sugar.
While it is admittedly confusing to have all these different flavors of JS, I don’t think this proposal is actually as radical as it seems.
Outside of browsers this is already how it works. Nothing is stopping LLVM versus GCC from adding their favorite language features, but it's not a disaster.
