"Last time I saw him (a few years ago now), he was working on wireless brake controllers. It's a very interesting exercise analysing the reliability of wireless brake controls, and computing that despite your natural horror at the idea, they're no more likely to fail than a brake cable is to snap."
I'd suggest that the likelihood of either is dependant on maintenance.
If you don't keep charging a wireless system it will fail catastrophically fairly quickly. This is particularly true of the 'actuator' end of the system.
If you don't maintain a brake cable then after many years it will start to fray - it will get harder to apply the brakes, and eventually one of them will fail - but by that stage most people with that little mechanical sympathy will have taken the bike to their bike shop for new pads.
It's easier to get a cable to snap if you manage to set it up very badly of course...
Then he omits to mention hydraulics...
I wouldn't trust wireless brakes on a push bike - but it's not just the 'wireless' bit that concerns me, it's the extra batteries. And with wireless you can always jam a signal - which in this case would presumably put the brakes on full, inevitably causing a face plant for anyone on an upright bike...