I know people are crying out for this, but I can only shudder inside at the unholy mudball messes that will result. Inheritance is one of those things we shouldn't let anyone use until they're 40 or so.
Well to be fair to myself, I was mainly making a joke. But the simple truth is that inheritance doesn't bring new power to the table, just syntax sugar, and with great sugar comes diabetes and painful death.
Classes is a big enough portion of sugar to change expression level of code. After writing ES6 few months I don't like to write ES5 again, when I have to, and there is a lot of people who think so. Arrow functions is the another (if not first) big thing which makes this feeling stronger, and it's just a syntax sugar also.
OO in ES5 looks less readable and less.. "native" than in ES6.
Hope in some ES version 'this' insanity will be fixed and all will be just fine with classes.
just for note: I have never used "extends" in ES6.