New Twiddle

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({

	data : [],
	scrollTimer : null,

	init : function()
	{
		var data = this.get("data");

		for (var x=0;x<1000;x++)
		{
			var obj = {id:x,label:"o".repeat(10) + "_" + x,vis:false};

			data.push(obj);

			obj = null;
		}

		Ember.run.later(this,this.make_visible,0,5000);
	},

	make_visible : function(idx)
	{
		var data = this.get("data");

		Ember.set(data[idx++],"vis",true);

		if (idx < data.length)
		{
			Ember.run.later(this,this.make_visible,idx,50);
		}
	},
});

application.template.hbs

{{#each data as |item index|}}

	{{data-item item=item}} 

{{/each}}

data-item.component.js

import Ember from 'ember';

export default Ember.Component.extend({

	itemComponent : function()
	{
		var item = this.get("item");

		return item.vis ? "item-visible" : "item-hidden";

	}.property("item.vis"),

});

data-item.template.hbs

{{component itemComponent item=item}}

item-hidden.template.hbs

hidden

item-visible.template.hbs

visible

twiddle.json

{
  "version": "0.4.13",
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.13.10/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/1.13.13/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.13.10/ember-template-compiler.js"
  }
}