I'd fully expect other car makers to move to an exclusive 48V setup at some point. They just do it gradually: For the new model a part is replaced by its next-gen successor that is incompatible anyway? Put it on the 48V bus. Repeat until the 12V system is done away with - or force the issue when there are only a few components left, or downstep the 48V to 12V right in front of them, once that's cheaper than keeping the remaining 12V system.
It'd be cheaper to delete the 12V bus entirely and add 48V -> 12V converters in front of legacy components, even if they needed several dozen of those converters.
I think all the wires/communication are but some of the devices attached are lower then 48V, some very low voltage, and some might be 12V. We will see when its taken apart.
