And in addition to all that the batteries are meant to solely power the aircraft in the event of a total failure of all other electrical sources - which does happen now and again, even on a four (not two) engine 747.
Not sure I want to see all those protections kicking in when the plane is just a few miles short of the threshold in an emergency situation. Or when the APU needs to be started up in the air.
That seems a valid concern given some 'solutions' seem to only be concerned with managing the fire rather than any effect caused by the failure of the battery.
Overall, it seems to be a fairly well understood problem in a discrete component of the plane. It's not like "wing failure" or a wiring problem with 8000 miles of cables. It's serious in terms of individual aircraft and the current fleet, but maybe not serious in terms of the future of the dreamliner project.