ES7 was developed concurrently with ES6. ES6 is also officially known as ES2015 now with ES7 being referred to as ES2016. Apparently the goal is to ship functionality to the language on an annual basis.
Not sure, but I think it's unique to JS b/c it's built into web browsers. Therefore, all major browsers vendors need to ok major changes to the language so that there isn't a severe fragmentation in version support. I think this is achieved via the standards committee.