The Avalung is a great tool to help increase your chances of survival if caught in an avalanche. However, it should not be involved in a decision making situation, ie; "well, this snow pack looks sketchy but I've got my Avalung so… lets go." building it into the pack is a great way to decrease this impulse.
Unfortunately Black Diamond will not license the lung to other pack manufactures, or sell a version that could be attached to an existing backpack in an effort to direct consumers to buy their pack. Good marketing, but It would be a better gift to the backcountry community to offer it in multiple ways. It is another great tool to have in the mountains and is a great innovation.