This is why the JS ecosystem frustrates me. We're talking about an ES7 -> ES6 transpilation, which I will then have to transpile again to ES5. And that's before we even hit the VM/JIT.
But note that it's shipped as a babel plugin, so you shouldn't even need to care.
What this really is is "use the currently-most-popular JS transformation toolchain to transform cool-JS to works-in-browser-JS". Whether part X is in the ES6 standard and part Y might end up in ES7 is really mostly besides the point.
Anyway, I agree, the sooner Kneden becomes obsolete, the better!
This isn't like TypeScript or CoffeeScript where you're always transpiling.