Also from what I've seen, the typical peripherals around a automotive uC differ greatly from a ARM "entertainment" SoC and that's whats the bigger difference. e.g. Infineon TC29xx http://www.infineon.com/export/sites/default/media/products/... vs Snapdragon 820 http://files.linuxgizmos.com/einfochips_eragon820_com_block.... Block Diagrams

In both of those chips the CPUs themselfes are the smallest part but the on chip peripherals differ greatly by usecase. The automotive has a great plethora of different busses and i/o (digital, analog, complex PWM, CAN, LIN, FlexRay) while the typical ARM core has less but higher bandwith IOs.

The other big step is backwards compatibility. Going to a completely different architecture is a bigger step than going from one iteration to the next one.

So probably even the "new" designs for 2020 may use the successor of the current generation of uC or SoC chips.