(1) have ONE pushable and turnable knob, somewhere - steering wheel, dash, doesn't matter (2) 25-30 one-word voice commands: "volume"/"louder"/"hotter"/"A-C"/"radio"/"front"
Want to turn on the radio? Say "radio", push button. Louder? "louder", turn knob. Cooler? Say "A-C", push button, turn knob. "Fan", turn. Maybe some white noise feedback while turning it, to indicate whether you're in the low range or high range. Done!
Also, I have a turnable+pushable knob in my car and it's frankly terrible because it's very easy to accidentally push when you're trying to turn.
What is far easier to do is to make it so that turning a knob says via audio what action is selected. Then you press a different button to confirm.
I have 3 years of experience with a CarPlay-enabled car, and Siri mostly just works as a voice interface. (But to your point, car makers' home-grown solutions are almost comically bad.)
Exactly. Judging by how they are managing to make the worst possible decisions wrt touchscreen offerings, I'm not holding my breath for siri-like voice activation from car makers