Anyway, with several years of practice we've seen some fairly reliable shutoffs developed. But any mechanical device is subject to bending/ breaking/jamming etc. not mention getting tripped at the wrong time or being subjected to flight forces that keep it open.
How about trying to develop a shutoff that senses continutity in the lines? I talked with one of the Europeans late last year about this. The electronics are fairly simple and could be very light < 1 oz. Some possibilities- the shutoff senses a signal that is sent up the lines from the handle. If the signal stops the shutoff closes. The shut off sense the capacitance between the plane and ground and trips if that changes. indicating a line break. Perhaps we could also send an IR signal to the plane like one of the throttle controllers. Lose IR, shut the fuel off.
Any electrical engineers want to take up the challenge.
Phil C