New Twiddle

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName:'Dynamic Components Example',
  currentModal: null,
  showModal: Ember.computed('currentModal', function() {
    return !!this.get('currentModal');
  }),
  actions: {
   	openModalA() {
      this.set('currentModal', 'modal-a');
    },
    openModalB() {
     	this.set('currentModal', 'modal-b'); 
    },
    closeModal() {
     	this.set('currentModal', null);
    }
  }
});

application.template.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{#if showModal}}
	{{#x-modal close=(action 'closeModal')}}
		{{component currentModal}}
	{{/x-modal}}
{{/if}}
<button {{action 'openModalA'}}>Open Modal A</button>
<button {{action 'openModalB'}}>Open Modal B</button>
{{outlet}}
<br>
<br>

modal-a.component.js

import Ember from 'ember';
import ModalComponent from 'demo-app/x-modal/component';

export default ModalComponent.extend({
});

modal-a.template.hbs

This is Modal A
{{yield}}

modal-b.component.js

import Ember from 'ember';

export default Ember.Component.extend({
});

modal-b.template.hbs

This is Modal B
{{yield}}

twiddle.json

{
  "version": "0.5.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "enable-testing": false
  },
  "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",
    "tachyons": "https://cdnjs.cloudflare.com/ajax/libs/tachyons/3.0.2/tachyons.min.css"
  }
}

x-modal.component.js

import Ember from 'ember';

export default Ember.Component.extend({
	actions: {
		close() {
    	this.get('close')();
    }
  }
});

x-modal.template.hbs

Parent Component <button {{action 'close'}}>Close Modal</button>
{{yield}}