New Twiddle

components.my-component.js

import Ember from 'ember';

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

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  "openTag": "<div>",
  "closeTag": "</div>"
});

templates.application.hbs

<h2>What I want: </h2>
<div>
    <button type="button">Button</button>
</div>

<h3>Here's sly7-7's suggestion</h3>
{{#my-component tagName="button"}}
 I'm a button
{{/my-component}}

{{#my-component tagName="div"}}
 I'm a div
{{/my-component}}

{{#my-component tagName="ul"}}
  {{#my-component tagName="li"}}1{{/my-component}}
  {{#my-component tagName="li"}}2{{/my-component}}
{{/my-component}}

templates.components.my-component.hbs

{{yield}}

twiddle.json

{
  "version": "0.10.5",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.8.0",
    "ember-data": "2.8.0",
    "ember-template-compiler": "2.8.0",
    "ember-testing": "2.8.0"
  },
  "addons": {}
}