It doesn't make sense to say that. Other languages had it from the start, and it has been a success. Immutable.js is 10% as good as built-in immutability and 90% as painful. Seal/freeze,readonly, are tiny local fixes that again are good, but nothing like "default" immutability.
It's too late and you can't dismiss it as "been tried and didn't get traction".
That's not what I said, and that's not what my reply is about. The value of immutability is known. That's the point of this post. The author isn't a TC39 member (or at least I don't think they are). They're doing what they can with the tools they have.
It's too late and you can't dismiss it as "been tried and didn't get traction".