The killer feature is the method of authentication. But to want it, you have to know a bit about public key cryptography. Not very much, nothing that can't be grasped by say a 12-year old. But it requires a bit of habituation and a change of mental focus for most people. It's a bit like getting people to take up Pilates, or skateboarding, or vegetarianism, or even personal computing, in a world where these things haven't entered the mainstream. There is no immediate market for it, but it's the sort of thing where a market could at any time emerge very rapidly.