Since not all existing AngularJS (1.x) projects can jump into using Angular (2+) and ng-upgrade may not be a feasible option for some, I created a seed repo in GitHub to demonstrate AngularJS working with webpack and ES2015+ syntax.
To me, ES2015+ syntax, in particular the introduction of modules (import / export) has ushered in a new era of writing JavaScript applications, including our good friend AngularJS.
By adopting ES2015+ syntax and following meaningful styleguide conventions like John Papa's, these effort can really go a long way to improving the readability and organization of an existing AngularJS app. Plus, if you can slowly migrate through the releases of AngularJS > 1.5, you can set yourself up for a migration path to Angular now.
This seed is not meant to be comprehensive, but just as a way to show that any existing AngularJS app can benefit from an ES2015+ upgrade, backed by webpack.
Hope to hear your thoughts and feedback!