This was the conclusion of an EcmaScript meeting in Oslo last month. Specifically, as Brendan Eich explains, three features – packages, namespaces and early binding – were considered
too heavyweight unsuitable for a browser scripting language. Here is Eich’s “Executive summary”:
The committee has resolved in favor of these tasks and conclusions:
1. Focus work on ES3.1 with full collaboration of all parties, and target two interoperable implementations by early next year.
2. Collaborate on the next step beyond ES3.1, which will include syntactic extensions but which will be more modest than ES4 in both semantic and syntactic innovation.
3. Some ES4 proposals have been deemed unsound for the Web, and are off the table for good: packages, namespaces and early binding. This conclusion is key to Harmony.
4. Other goals and ideas from ES4 are being rephrased to keep consensus in the committee; these include a notion of classes based on existing ES3 concepts combined with proposed ES3.1 extensions.
… you can forget a lot of what you learned about ECMAScript 4, previously. Many of the complicated concepts contained in the language have been tossed. Instead there is a considerable amount of effort going in to making sure that new features will be easily duplicable through other means.
It is also presenting Adobe with a tricky problem, as it implemented much of an earlier specification for EcmaScript 4 in ActionScript 3. Rather than being a standard language, as Adobe had planned, it looks like this will now be more of an Adobe language. I doubt this will have much practical impact on developers.
PS Brendan Eich has commented below.