New Twiddle

application.controller.js

import Ember from 'ember';

const DEFAULT_MODEL = {
  relationship: {
    isFulfilled: false,
    someValue: false
  }
}
export default Ember.Controller.extend({
  appName:'Ember Twiddle',
  model: Ember.copy(DEFAULT_MODEL, true),
  
  actions: {
    changeModel() {
      this.set('model', Ember.copy(DEFAULT_MODEL, true));
    }
  }
});

application.template.hbs

<h1>Welcome to {{appName}}</h1>
<br>

{{input type="checkbox" checked=model.relationship.isFulfilled}} isFulfilled<br>

{{input type="checkbox" checked=model.relationship.someValue}} someValue<br>

<br>

<button {{action "changeModel"}}>Change Model</button>

<br><br><br>

{{#if (async-not model.relationship 'someValue')}}
  Showing some value
{{else}}
  Not showing some value
{{/if}}
  

helpers.async-not.js

// app/helpers/async-value.js
import Ember from 'ember';
const { 
  get, 
  addObserver, 
  removeObserver 
} = Ember;

export default Ember.Helper.extend({
  installObserver(relationship, key) {
    if(this._installObsRelationship !== relationship || this._installObsKey !== key) {
      this.uninstallObserver();
      this._installObsRelationship = relationship;
      this._installObsKey = key;
      addObserver(this._installObsRelationship, this._installObsKey, this, this.recompute);
      addObserver(this._installObsRelationship, 'isFulfilled', this, this.recompute);
    }
  },
  uninstallObserver() {
    if(this._installObsRelationship && this._installObsKey) {
      removeObserver(this._installObsRelationship, this._installObsKey, this, this.recompute);
      removeObserver(this._installObsRelationship, 'isFulfilled', this, this.recompute);
      this._installObsRelationship = null;
      this._installObsKey = null;
    }
  },
  willDestroy() {
    this.uninstallObserver();
  },
  compute([asyncRelationship, key], hash) {
    this.installObserver(asyncRelationship, key);
    return asyncRelationship && !get(asyncRelationship, key) && get(asyncRelationship, 'isFulfilled');
  }
});

twiddle.json

{
  "version": "0.4.17",
  "EmberENV": {
    "FEATURES": {}
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.2.0/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.2.0/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.2.0/ember-template-compiler.js"
  }
}