With a 300 VDC battery pack, any idea about what voltage (or voltages) the accessory bus will run?
Here's my guesses:
12 VDC where ever practical so off-the-shelf devices can be used.
They are re-engineering wiper motors, heat pump compressors, and other high wattage accessories to get the watts down, so I'd guess they might as well go to higher voltages (maybe 48 VDC?). The lower amps would reduce motor cost and wire sizes.
I suspect they'll need a DC-DC converter to step down the voltage, as just tapping a few cells off the 300 volt pack for the lower voltages would unbalance the cell loads.