I don't understand how a PCB+MCU can reduce the copper wiring. The bulbs will consume the same amount of power requiring the same thickness of copper wiring, no matter if it's 10 separate thin wires, one for each bulb, or just one wire, but 10 times thicker (by section area and weight/meter, not diameter).
Common power wire will still require one or two extra wires for CAN, so it would make sense only as replacement for bundles of 3 or more wires going to the same place.
you have a single bus in a ring topology instead of a star network of wires coming from a central location. much less wire and with most indicators and even some headlights being LEDs the current carrying capacity of the +12V wire can be much smaller. GND is the metal substructure and the CAN (or LIN) bus is just two small gauge wires.
much cheaper and much less wiring needed if the bulbs (or bulb holders) can receive commands themselves.
Without a board: you need a big power wire for low beams, a big power wire for high beams, a smaller power wire for turn signal. And that's all you can do.
With a board: you need a big power wire for everything. And a two tiny wires for CAN--so you're already ahead. If your beams can move, or be directed, or have LEDs that can be modulated, or have a washer, you start coming out WAY ahead.
Common power wire will still require one or two extra wires for CAN, so it would make sense only as replacement for bundles of 3 or more wires going to the same place.