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.