For starters, this will enable client (browser) software development in a language other than Javascript/ES6. With, probably, a plethora of compilers to choose from, some of them giving better optiimizations than others.
I think this will make an explosion of more browser-hosted applications, with much more power than before. And will make many more programmers go into serious frontend app development.
Also, as a personal wish of mine, this enables the possibility of being able to program on the language of your choice, both in the browser side and on your server side. For example Haskell/Haskell, Common Lisp/Common Lisp, Clojure/Clojure, Racket/Racket Python/Python, etc. And i mean using in the browser the FULLY FEATURED version of the language, not a subset or a limited version like ClojureScript, PyJS, Transcrypt, etc, but a full version of the language supporting the full libraries available for it.
This also gives us a little step forward in liberating ourselves from being tied to the mainstream operating systems: Windows, Apple X, Linux, BSD, because more and more apps will target the browser environment, not the operating system directly.
Roll your own operating system and still keep compatibility with most apps!!