This seems like a very HN-specific use case. It's not surprising that automakers don't have APIs that let customers host servers that they use to remotely start their vehicles. Security is obviously a huge issue, and almost no one cares about remote starting that much, and has the know-how to implement relay servers and such.

I'm not happy with how consumer choice is boxed in by automakers, but for sensitive systems like ignition, I don't think that their approach is unreasonable.

What do you mean HN-specific? I don't understand how cars got to require permanent cellular connections in the first place while Bluetooth would've been enough

I was referring to the fact that a very small sliver of the population would be interested in running their own relay server, or even figuring out what that means. They just want to press a button and have the car turn on.