I thought Straubel said that the Powerwall was meant not for offpeak storage but for emergency backup.
EDIT: This is a baller feature:
"Always Connected: Monitor your solar energy use in real-time and receive alerts when Powerwall is preparing for cloudy or severe weather."
They're performing weather forecasting, and then ensuring the Powerwall has charged up for a possible outage event. Brilliant.
This lets you have best of both worlds, with a minor tradeoff in unpredictable outages you have slightly reduced runtimes.