This seems to require a near-by powered wifi device to aide in association of the passive device. For large deployments, that would require many powered units. In addition to that, there are requirements for multiple MACs, which may also lead to problems with limits in some networks. This is all clever, but it doesn't seem practical to me since the passive device depends on a near by powered device to do anything. I have worked on sensor networks with battery powered wifi devices. It's certainly tricky.