I don't even want a modular computer slot - I just want a built-in 'remote' display panel & speakers. Just setup a peripherial that can be wirelessly or usb/lightning cable linked that also transmits the touch info back to my phone and plays sound.
Maybe a switch to flip the display to access direct car controls (but really just give me hard-buttons/dials etc for climate control and keep the consumer electronic part simple and separate).
Extra points if there's a standard for sending car control api calls back and forth to the phone, but 90% of utility could just be handled with a remote touch display.