I super agree with everything, with the probable exception of Seatbelts. Is that even a standard with a concern for compatibility? I'm not sure if I can plug the belt of one car to the seat of another. Would be cool, I guess. If my seatbelt ever breaks, I guess that would mean I can obtain a "standard" seatbelt without worrying about compatibility.

There are "heavy" people who carry a seat belt extender because most cars don't have a long enough seat belt without it. So yes there is a compatibility concern.

Though there isn't a standard. Different manufactures use different connectors, not to mention air planes.

There's a standard in that cars must have them, and they must have certain properties in terms of abrasion, strength, surface area etc.

I agree with your general sentiment but NEMA 1-15 must go (it kills a few people each year) and so must IPv4 (it spawned NAT which destroyed the Internet).