The value proposition of CAN bus is that peripherals can be scattered around connected by two data lines and a power wire. Dumb peripherals need more wiring.
Can is a great idea... But in practice the hardware to connect to the bus is ~10 cents, whereas the cheapest microcontrollers are ~1 cent. That means if you want thousands of connections for every peripheral, the costs of CAN transceivers really start to add up.
They are deviating from that already, aren't they? If they use one ECU per zone, then the peripherals in that zone can't be connected via CAN bus, otherwise they would need their own controller.
