I'd advocate most people avoid this if their intention is to write an app. As an alternative, I'd suggest evaluating create-react-app [0] or preact-cli [1] if you're looking for something lighter. The lack of testing setup and module support in this kit feels like a regression, although I'll concede that it really depends on your use-case.
I've been using webpack [2] for a few years and wouldn't willingly go back to this style of writing web apps. Once you learn how to use it, the world is your oyster. You can write a loader or plugin to achieve pretty much any kind of requirement that comes your way.
Consider replacing sass with cssnext [3], or even directly using postcss along with the few plugins you need. As an example, you can use native css variables during development and compile em away for production. Another great addition is the :matches selector, which makes for much cleaner selectors in certain cases. I never really found much value in most other sass features.
Instead of running imagemin as part of your build process, consider installing imagemin-cli [4] and applying optimizations before checking in images. That way it only has to done once, regardless of how many times someone checks-out your repo.
Even if you enable ES2015 compilation with babel, you don't get any polyfills. That means trying to use standard ES2015 globals like Map, Set, or Promise will not work on older browsers. If you're gonna tell people they can add ES2015 support by changing a single line, it would seem prudent to mention this gotcha.
[0] https://github.com/facebookincubator/create-react-app
[1] https://github.com/developit/preact-cli
[2] https://webpack.js.org
[3] http://cssnext.io
[4] https://github.com/imagemin/imagemin-cli