Imagine that you:
- Are an engineer.
- Have to read and learn this small technical specification
- Then you have to ask many of your questions to understand what exactly you need to write and how it should work.
- Are working on free product - browser, and, probably, won't get much paid for that. You also won't have much team members helping you.
- Have other projects and tasks to work on.
- There are a lof of bugs you have to fix also.
- There are priorities in your tasks and usually other small group of engineers (couple of millions of engineers around the world) is voting which features should be implemented first
- Imagine that you also have to participate in a lot of discussions and sometimes support and answer questions from that millions of engineers
- Need to support and test your code on windows, MacOS, iOS, Linux and many other platforms
- If you forgot #1, you are just a one engineer
Hope, now you understand - why it takes so long...
Answering your 2nd question - when. You should ask it to browser developers directly, follow the roadmap and vote for the next features yourself:
Web Platform Status links
P.S. ES6 is almost fully supported in all platforms.