Giving developers the ability to use the same technology stack has a lot of potential. While this will not work for every type of web application, it will make things easier for front end developers working with their back end developers.
When building web apps, there are many architectural decisions. In today's development world, allowing for rapid development, constant iteration, speed, robustness, etc. Lean and agile are the key. Selecting technologies that facilitate these objectives are not easy.
This is useful for a number of reasons:
The biggest challenge with non-blocking programming is when you get into very complex callbacks mechanisms. But with ES6, you will see the use of promises and generators. Both are much better at solving the typical callback challenge. And since you do not need to worry about browser compatibility on the server, you can start using ES6 with Node right away!
Plus, the number of Node modules that are becoming available on NPM is growing like crazy. So chances are, many of the modules you may need for your application are already available, or least you have a good starting point.
Node has also become a great tool for front-end developers. Bower, a good front-end package manager, Libsass for compiling Sass, Grunt for automated build tasks, Mocha for unit testing and many other tools are now built on Node.