Polymer 2 redux + ES6 import

configureStore.js

import { createStore, applyMiddleware } from 'redux';
import thunkMiddleware from 'redux-thunk';
import { composeWithDevTools } from 'remote-redux-devtools';
import reducer from './ducks';

const configureStore = (initialState) => {
    const enhancer = composeWithDevTools(
        applyMiddleware(
            thunkMiddleware,
            // logger
        )
    )
    return createStore(
        reducer,
        initialState,
        enhancer
    )
}

export default configureStore;

my-app.html

<link rel="import" href="redux-mixin.html">
<dom-module id="my-app">
  <template>
    Hello world!
  </template>
  <script>
     class MyApp extends ReduxMixin(Polymer.Element) {
        static get is() { return 'my-app'; }
     }
  </script>
</dom-module>

polymer.json

{
  "entrypoint": "index.html",
  "shell": "src/my-app.html",
  "fragments": [
    "src/my-view1.html",
    "src/my-view2.html",
    "src/my-view3.html",
    "src/my-view404.html"
  ],
  "sources": [
    "src/**/*",
    "redux/**/*",
    "images/**/*",
    "bower.json"
  ],
  "extraDependencies": [
    "manifest.json",
    "node_modules/redux/**/*",
    "bower_components/webcomponentsjs/*.js"
  ],
  "lint": {
    "rules": ["polymer-2"]
  },
  "builds": [{
    "name": "es5-bundled",
    "bundle": true,
    "js": {"minify": true, "compile": true},
    "css": {"minify": true},
    "html": {"minify": true},
    "addServiceWorker": true,
    "addPushManifest": true
  },{
    "name": "es6-unbundled",
    "js": {"minify": true},
    "css": {"minify": true},
    "html": {"minify": true},
    "addServiceWorker": true,
    "addPushManifest": true
  }]
}

redux-mixin.html

<link rel="import" href="../bower_components/polymer-redux/polymer-redux.html">
<script>
  import configureStore from '../redux/configureStore.js';
  const store = configureStore({});
  ReduxMixin = PolymerRedux(store);
</script>