ECMAScript 7 is the next evolution of the ECMA-262 standard. New language features are proposed already as the draft of Edition 6 is feature frozen and nears its completion. You can see the current proposals on the tc39/ecma262 GitHub repository.
Current issues with the specification process are planned to be solved by introducing stages and champions for feature sets. Also, a two year release cycle of the standard is proposed. For more information about the post-ES6 specification process, see this presentation by Rafael Weinstein.
A channel for feedback on ECMAScript standards is es-discuss.
Experimental features
The following features are already implemented, but only available in the Firefox Nightly channel:
Additions to the Array object
Additions to the ArrayBuffer object
New TypedObject objects
New SIMD objects
Features with ongoing stabilization
The following features are supported beyond the Nightly channel, but ongoing specification and implementation work is happening. Features which were originally in the ECMAScript 6 draft and got postponed to ECMAScript 7 are likely to appear here.
Expressions
Features not yet supported
The following features are not yet implemented, but targeted for ECMAScript 7.
Object.observe()(bug 800355)