Barking mad.
Why were you "horrified" to learn of the Airbus' BSCU? It has two independent channels. I'm pretty sure one can be inoperable on MEL. The backup brakes are sufficiently independent to allow it, steering likewise. BSCU. Works well, lasts a long time.
Back to the 787...
I think there is too much lost in translation with that Japanese report.
1. The main bat DOES have a "valve" or diode. So what do they mean.
2. The APU bat supplies the nav lights when the tow switch is selected. Under normal circumstances they are powered from a DC Bus. (I think, no schematics handy so I could be wrong.)
Miswiring or dodgy switch/breakers/contactors?