It's complicated by two factors: 1) The head unit controls far more than maps and entertainment; it's also wired into climate controls, seat positioning, etc. t

It's complicated by two factors: 1) The head unit controls far more than maps and entertainment; it's also wired into climate controls, seat positioning, etc. that require direct access to other vehicle hardware. 2) Head units and associated services are a profit center for OEMs. Switching to a "bring your own tablet" model would cost them a fair amount of profit.