New Twiddle

router.js

import EmberRouter from '@ember/routing/router';
import config from './config/environment';

const Router = EmberRouter.extend({
  location: 'none',
  rootURL: config.rootURL
});

Router.map(function() {
  this.route('dashboard');
});

export default Router;

routes.dashboard.js

import Ember from 'ember';

export default Ember.Route.extend({
  model() {
    console.log("Dashboard route is loaded by default");
  }
});

routes.index.js

import Ember from 'ember';

export default Ember.Route.extend({
  redirect() {
    this.transitionTo('dashboard');
  }
});

templates.application.hbs

Parent application.hbs
<br>
{{outlet}}
<br>
<br>

templates.dashboard.hbs

Dashboard is loaded

twiddle.json

{
  "version": "0.14.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "2.18.2",
    "ember-template-compiler": "2.18.2",
    "ember-testing": "2.18.2"
  },
  "addons": {
    "ember-data": "2.18.2"
  }
}