Note: These were never sold in the North American Market, but they're extremely common in Australia, South Africa, etc.
Naturally, I can't find any links to the info...
Just built a car without a single relay. I used PMUs (basically boxes of mosfets and current sensors AFAIK).
Wouldn't a more important question be how does the failure mode change?
With AC, the arc will self-extinguish a half-cycle after the switch opens. With DC there is no cycle, and contacts can be completely vaporised in tens of milliseconds.
Commodity switching components are usually rated "30V DC, 250V AC" for this reason.
It is possible to design switches so that even DC arcs self-extinguish, but the result is expensive and not as reliable as one could wish.
If cars had been invented after 1980, they would probably use solid-state switches except for the very high current circuits such as the starter solenoid and headlights. (Transistors were around a lot earlier than that, but engineers are sensibly cautious about new technologies.)
Edit: To answer your question directly: no. Cost is prime.
You could also just switch the HV (400V+) bus directly down to 48/60V as all the high current devices motor/ac/power steering etc run off the HV bus and you would just be left with lights, entertainment and servos on the low voltage side. The 12V battery is probably a bit silly when you have a 50KWH main battery and 97% switching conversion efficiency regulators and I am guessing it may disappear in the next 10 years
I meant to the customer or owner, over the normal lifetime of the vehicle, not to corporate accountants that translate pennies into millions of dollars.
"More expensive" presumably is a small amount per car; the average new car in the US is over $40K.
6 and 12 V electric systems in vehicles came about because lead-acid batteries made sense in this application, and cetpar. a higher voltage lead-acid battery is overall costlier to manufacture, because it contains more individual cells. Another big thing is that there are many switches and relays in a car, and those often switch significant power. E.g. the light switch for the headlights has to deal with around 200 Watts total for incandescent/halogen headlights, indicators are like 15 Watt each front and back, the starter motor requires a tremendous amount of power, and has a very robust power switch built into it.
All of those switches become much more expensive when you increase the voltage. DC at 12 V and sizable currents is something you can reliably switch with mechanical contacts without costs going through the roof.
Being able to use 48 V for everything in a car is more or less dependent on using silicon switches for everything, not something that was possible in the past. The reason why legacy ICE cars (all ICE cars are now legacy) stick with 12 V is because everything is 12 V, and everything would have to change for the new voltage.