Although in principle it is a similar concept to namecoin + PGP, in practice at least for our device, that felt like a hammer to crack a nut, "How could this operate if the device was carried to one of the non-3G countries i.e. with no direct internet access? How could we syncronise the chain in a low bandwidth environment, if at all? Could at least some of the chain be pre-loaded at the factory? What would the risks be if it was?". 

These are just a few of the practical considerations that we are addressing, and our feeling is that when we can get the proposed distributed ledger to work properly at "the lowest common denominator" level, then everything above is easier. 

On one other point, I don't ever see the Bitcoin software using a second blockchain, like namecoin, in order just to provide safe communication of a non-face-to-face, person-to-person, pay-to address (far too many hyphens), but I do see some other standard emerging that provides the equivalent of BIP70 for this use case.  

In this context, when we posed these questions, "Why do we have to provide a reward for a ledger of information? Why do we have to wait for confirmation when no money is at risk? What is the worst that can happen if your device key is discovered or replaced?", it did not make sense to include all the incumbent coin stuff just to arrive at a distributed ledger for a set of ultimately disposable keys.