There's a step between making untamperable black-boxes, and designing for repairability: don't use anti-tampering measures, and make available the code, schematics, and documentation the company itself uses for repairs.

A locomotive or car also have a high amount of engineering and expertise poured into them, and that fosters a third-party maintenance industry. No one would accept a fully black box locomotive or car that only the original manufacturer can open and repair, for whatever they want to charge. We are becoming too comfortable with monopolies.