Personally, I don't
I've never quite understood why people want to watch extended gameplay videos of upcoming content. I mean, if you're excited and want to play it, why would you want to spoil a long chunk of it? Conversely, if you couldn't care less about it, you're probably not going to watch in the first place, right?
Regardless, that's neither here nor there (or maybe it's both here and there) because you can totally fire up the first half hour of Arkham Origins: Cold, Cold Heart DLC if your cold, cold heart so desires. I wouldn't, but the choice is yours.