What would be nice is if Apple and Google and Microsoft got together (yeah, right
) and came up with an in-car hardware specification. As far as I'm concerned your phone should run the whole thing, so you're basically talking about just a screen and a series of controls (buttons, dials, whatever). Come up with 2-4 standard configurations, similar to how the Apple MFi spec works for game controllers. Manufactures have a few options for the level of support they want, and can customize the controls any way they want as long as they comply with the spec.
Then, the phone companies handle the software side, completely. Apple, Google, and Microsoft each come up with their own in-dash UI (assuming they want to). Then, everyone who drives gets their phone's custom experience with access to all their data.
The car manufacturers could even still produce their own in-dash systems as a base system, but if you plug a phone in, basically override all of it and drive the screen from the phone. Then Apple, etc. should allow them to write apps which can access car-specific things like engine monitoring, backup cameras, etc.
Because right now I feel like they are daring us to take a saw to the dash and just mount an iPad in there.