At first glance, this looks like a broken combo, but you need to keep in mind several things. The engine card (Lorewalker Cho) gives a copy of the spell played to your opponent. They can choose to do what they wish with that spell, but you'll only get another copy if they play it. In a real game (as opposed to this demonstration of a funny trick), you'd equally be able to cast the spell on your own minions, so if anything it's equally ridiculous for both players.
You could also choose to use the cards as "fuel" for spells that make you discard a card when you play them, thus stopping the combo from going anywhere. Also, there's removal cards that will take out a minion regardless of their health, so Cho could be shutdown right fast (and you probably should make him a priority target if your opponent plays him). With a properly-tuned deck, Cho might be overpowered... but I'm not sure the cards are available to do that (at least not yet).