And yet a good part of ES4 been realistically implemented in ActionScript 3 and used by many developers for over a decade.
And those namespaces in AS3 (much simpler than in ES4) I think are quite a good idea, they allow to control what is visible or not and/or to switch which implementation you use.
For example when some AS3 builtins do not support some methods defined later in ES5.1 then ES6 etc.
ES5 function trim():String
ES6 function repeat(count:Number):String
So yeah you not gonna use namespaces everyday for everything, but they do have allow to solve specific problems while "programming in the large".
And those namespaces in AS3 (much simpler than in ES4) I think are quite a good idea, they allow to control what is visible or not and/or to switch which implementation you use.
For example when some AS3 builtins do not support some methods defined later in ES5.1 then ES6 etc.
So yeah you not gonna use namespaces everyday for everything, but they do have allow to solve specific problems while "programming in the large".