Safety, risk of losing lives, is a factor missing from the constraints imposed on PC manufacturers. Safety may play a larger role as an obstacle on this idea getting real traction.
That factor is already imposed on individual auto manufacturers. If anything, standardized part designs would probably increase safety and lower manufacturer risk.
The problem is that far too many people don't do product research beyond "Does it fit?".
I've seen a good amount of destroyed audio equipment resulting from the owner failing to do compatibility research beyond verifying that two components could be connected together. "What's an ohm? Do I need one of those?"
I've seen people get the most baffled faces from not being able to pass a high bandwidth signal through the hundreds of feet of hilariously thin uncertified HDMI cable that they just ran through their walls. "But the box said high speed!"
Interchangeable batteries in cars would mean that drivers are only one el cheapo Amazon third party generic out-of-spec "compatible" battery away from stopping at a red light next to a moving bomb.
When I read "interchangeable batteries" I imagine a pretty simple procedure: open hatch, pop out old battery, put in new battery, close hatch.
When I read "install car parts" I imagine a procedure at least an order of magnitude more difficult requiring knowledge and experience working on automobiles.
Changing batteries is a task nearly all people have done at least once by the time they start driving. If changing the batteries in your car is as easy as changing the AAs in your Game Boy then I imagine many people would be willing to do it without thinking twice.
If it is truly that simple then I think the risk of screwing it up is also considerably less.
I mean, you know, it's not the same size and doesn't serve the same purpose, but today people's cars have batteries in them and you can walk into Sears and buy one. I assume the battery for an EV is huge and not conveniently located though.
In Germany at least cars are checked and licenced by TUEV at regular intervals and after tuning (but not after servicing?). The owner has to pay for the check up, too, if I remember correctly.
In the United States this is up to the individual state, but typically you have to have a once-yearly inspection of your car. Some states will check that various parts of your car are in good working order, others basically want you to not have a check engine light on or be spewing too many fumes. There's no responsibility to even notify anybody that you or someone else has modified your car and there's no problem as long as the modification itself isn't illegal (even then people sometimes just pay the tickets and keep driving around with illegal modifications).
I spent a year in Japan and the contrast between Japan in the US as far as the average age/condition of cars you see on the road is quite striking.