I don't understand why Apple doesn't just make their own head unit. A double-DIN chassis with a place to snap an iPhone into the front bezel. Most "integration" systems unnecessarily duplicate the screen and touch controls, and provide a less convenient and intuitive user interface. The phone itself already provides everything needed. Maybe include a big knob or two for volume/bass/treble/tuning etc.
Provide interface units for common steering wheel controls, or just allow third party suppliers to sell them.
If/when the form factor of the phones change, one can change the "deck" the same way one swaps out any car stereo unit.
This would have the enormous benefit of being something one can install in ANY car.