Vitalik does make a solid point regarding the computational/battery cost DAGs place on each participating node, but as David Sonstebo argued in an Ether Review podcast recently this cost will be very negligible because the ASICs that will eventually be required for a fully functioning IoT network will consist of no more than a few thousand logic gates and the hashing power required should theoretically be spread out among billions of devices. He also pointed out that he is very optimistic this ASIC will become an industry standard in processors and he revealed that major manufacturing firms have already reached out to the Iota foundation regarding this ASIC integration.