Perhaps you're right, and I merely remain wholly unconvinced, though I acquiesced in the OP that perhaps it will be necessary. Optimizability dictating language features to this extent is the tail wagging the dog. I think this would undermine the ecosystem by creating a subset that is neither Java nor JavaScript, neither safe nor dynamic; a lowest common denominator of sorts that may do more harm than good in the competition with native.
This is pure speculation on my part, but I wonder if a lot of the Google devs involved in JS in one way or the other just aren't that used to writing it.
It's this quote that caught my attention
Optimizability dictating language features to this extent is the tail wagging the dog.
AngularJS is another project that strikes me as being heavily Java inspired (although it's neither expressive nor performant), almost as if its authors are used to writing desktop applications in Java or C# and just wanted to port their experience to the browser.
It's as though the authors of Gmail or Google Docs are not people developing these other things.