Has this been attempted yet by any manufacturer?

Do Apple and Google voice assistants work with Apple Play and Googles services included with newer car entertainment systems?

You could in theory integrate an Amazon Echo dot into a car fairly easily. It's small, powered by 5V DC via USB, and can connect to a cars speaker system via bluetooth. But it's it worth thr bother? With my phone in the car I could just ask the Google Assistant something. But I do find Alexa easier to use in the house.

Voice controlled spotify f.ex.

My car does have limited voice control built in, but it doesn't talk to you, it just carries out commands such as changing radio station, switching mp3 album or changing CD. Quite limited by contrast. I can't ask it to set the sat nav destination f ex. I have to enter that manually. But then my car is from 2007 so back then voice control was very new. Voice controlled sat nav is much easier on my phone, but then I prefer the sat nav built into my car.