When I read this, my first thought was: Why do these ECUs have any deep logic at all? I would have expected all logic to be centralized at one point (or in a few points, but with each domain localized to one of them), and everything at the edge be dumb(1) port extenders. That's a single point of failure, of course, but as far as I understand the zonal approach has those too -- multiple SPOFs, actually. At least when it's a single SPOF, that problem can be better mitigated.

(1) "dumb" meaning no decision-making logic. It could still mean a lot of decision-less logic, from button debouncing to input signal filtering/processing and outputting compressed audio streams.