[usrusr]

The cost lies in replacing the 300$ phones where the switch breaks (earlier than expected).

Cameras are easier, blocking light is even more low-tech than closing a circuit. Unfortunately, cameras are already the limiting component in the current craze for ever thinner devices, so adding a slider on top would not be very popular. Theoretically, cameras could also be physically disabled by shifting some elements that are already there out of the optical axis. The precision requirements to reliably restore it to working condition would be insane.