It's the things like power management ICs, that have to deal with much larger currents and voltages, that are problematic, and you can't respin those on smaller node, and that's before you go for automotive grade tolerances.
That new MCU with new safety certification (and there's a lot of those going on, even a layman like me can see a push for equivalent of Integrated Modular Avionic in automotive) is going nowhere if it can't get power.
28nm by today's standard is already a very old tech. maybe the car vendors should move up
- Would require a redesign.
- Certain parts of the die cannot be shrunk: bond pads, esd protection, output drive transistors.
- Certain parts of chips are designed for proprietary processes (eFLASH, analog)