The most recent quote from Gabe that I've heard was basically this:
"The developers have full access to that feature and there is no work involved in adding it since its already in the engine. If they feel like it fits or they have a place for it they will add it in..if not then they won't. We've learned that these gameplay mechanics are fun but that its best not to forcefully work them in but rather let it flow naturally. Trying to force it often shows through in the final product and we've had some amazing results from just letting things take their natural course...so thats what we've decided to try doing from now on."
-my paraphrasing from a GameTrailer's interview








