Yes, I understand that you were speaking about the future. I sometimes wonder, if it is going to take complete redundant systems/sensors on these electric/electronic parts, so a computer could "check/verify" one system or its readings verses another sensor/s, but that cost more money. = somewhat like electronic engines, for the marine propulsion industry = they must provide a second backup system with minimal sensors and 2nd ECM to control an engine, if the first system goes down/fails.

When you are out on the ocean, and maybe in a storm or storm coming , with human lives on the line; this is required/mandated equipment, for electronic engines.(that's my understanding)

About your frustration, of a service guy not having any parts, arriving at a field job; I blame the management and/or their ability to interview and record customer's complaint right at the very first, initial phone call when customer asked for field service. With a decent interview and some notes, a mechanic should be able to show up with a few common parts. (Not uncommon to take $500-$3000 of parts with service truck, before leaving, especially on jobs over 1 hour away) Many times, foremans will get customer's cell phone numbers, and have that mechanic call customer before they leave the shop; but there can be a fault with that too = 1: makes foreman lazy, and 2: customer may not be near "failed" equipment 15 minutes to 2 hours later or so, when a mechanic can finally get finished with his current job, and has time to call customer.

Also, a good foreman, should give some good recommendations on parts to take(for a field job), because he reads service reports, about all failures and fixes, for everything that goes threw the shop, after repairs = should see trends between customer complaints, models, and final repair parts.

 The Dealership parts dept. HATES this(preordering parts), because it causes, twice as much work, for them to credit back all unused parts(paperwork, inventory, handling everything twice, etc)