> If a miscreant tries to snatch your machine and run off with it, the cord would pull out and the remaining USB key would trigger a udev command
And the USB key wouldn't pull out?
If the answer is "yes but pulling out the whole USB key triggers the wipe command anyway" ... well then you can make literally the same thing out of a regular $5 USB stick and some chain? The whole "run commands on plug/unplug" thing is literally what udev already does for all devices.
If the answer is "no it'll stay in the USB port", no, I rather doubt it will - unless it's a brand new laptop which hasn't had much USB intercourse yet at all. Or unless the special USB key is glued in, or customized in a way that is unlikely for $20.