But charge the capacitor with what? That's the point. If it doesn't kill the data immediately upon pushing the button, even when unplugged, it's useless unless some bumbling idiot thief/cop/agent plugs it in before just disarming the button.

And as for fully physical, do tests with what? Another computer? Its a memory storage device with only an I/O driver and basic firmware. There's no CPU to separately run software to detect if the components are destroyed. And if there were, that would have to be physically/electrically separated from the short that is going to kill the device and then physically reconnected, which would mean some kind of mechanical device most likely. Now were getting into a huge device, not a flash drive. The device already has capabilities to read and write data. Very easy to add a chip to give that random data to write over the existing data and a lot less power than a processor and motorized components.

And again, it doesn't solve the redundancy problem. Single point of failure is always going to go wrong at least one in some number of cases. Even top of the line components and the best quality control available can't beat redundancy and it's way, way cheaper.