Doesn't seem vague to me. No specific car will even be announced as supporting this until late next year. Which means no car will be running this in 2022.
Likely, the first cars that actually ship this will be December 2023, or more likely Q1 2024. A good quarter into iOS 17's lifecycle. Apple just about never ships anything earlier than they announce.
Apple may well be finished on their end before then, but manufacturers will have to adjust their own systems to accommodate the extra data calls, and to respond to the car-owned functions that this will expose to the phone's touch controls. That's likely a many-month process involving collaboration between the auto makers and Apple. Many automakers have probably already set in stone their software plans for the 2023 model year.
This is a lot more complicated than just turning over a screen or portion of a screen to be an external display for the phone.
Meanwhile, third-party developers will need to adjust their apps to be compatible with all the customizable widgets and such. Thus, the "sneak preview" and new developer tools being released now.