48v and the ethernet are not totally related, you could have a 48v car with the same wiring as before (just thinner wires which is the big saving for 48v). Ethernet allows even more saving on wire as you don't need point to point wiring for many specific features, you can just put a node which connects to the network and does the function you need. Old school wiring looms had a lot of point to point wiring on them. My suspicion is that future ones will be really simple as they will need only power and comms, with all the complexity offloaded to the network devices, as it were.