Having spent a long time with Java I believe I understand the limits of this style of coding; in my considered opinion, composition is almost always better than inheritance. This is true regardless of the type of inheritance, be it prototypal or class-based (in appearance or reality). Therefore, adding features to JS to make class-like inheritance slightly better is not a trade-off I would make, favoring a simpler language over a feature who's use shouldn't be encouraged.

Probably not ES2018, but 2019 is looking likelier now thanks in part to excellent work by Daniel Ehrenberg (@littledan).