I think it is a monumentally stupid idea. What if the "breaker" is the first thing to fail? What if a customer figures out how to bypass it thereby creating a larger safety issue?
If the device has an increasing risk over time of suffering catastrophic failure which could spread, then design in safety in depth. Typically this involves metal shielding, fusible links, and fire resistant materials but design counts as well if you consider fold-back current limiting and crowbar circuits.
In my post, I said that I did not agree with my custome's idea, but I actually I do not believe that it is a "monumentally stupid idea".
I'm talking about 30 to 40 years old power amplifiers. The simple fact that they are still working (maybe with some problems, a dryed-up capacitor or two) confirms that the original design (the designer is retired, and well alive at the age of 92 years) was sound and safe and "state of the art".
My new car forces me to change oil at some intervals, and if I do not oblige, after about 1000 km from the first signal the engine will not start.
One of my CAD programs says that the licence has expired (don't remember of a time limit, but cannot find the original papers) and does not work anymore.
I this really different from some "part" with a limited life that will break without other damages before any other part, and will require some technician to open the rack, check cables for undamaged insulation and rodent's bytes, and some unexpected work from an unknown and incompetent technician?
I know the end users: as was pointed out by SirNick some posts above, it is practically impossible to program any preventive maintenance with the "standard" customer: they simply refuse the idea.
Another example: I have a friend who was in TV service, for a BIG manufacturer. He showed me a board that was populated with 1/8 W resistors, that were overheating by design.
The standard failure was after 3 years of service. He replaced with 1/4 W parts, and the sets are still working after many years. Was this BAD design, or planned obsolescence?
Following my advice, my customer will write a letter to the owners of the oldest systems, and disclaim any liability for any damage. His lawyer is working on it.
Best regards