SolarCity installed the PV system, so I figured it'd be easier for them to continue with the upgrade. But it sounds like things are kind of a mess over in Tesla/SC land these days, so who knows...
In particular, how does an AC coupled system handle the case where the battery was fully discharged before sunrise? The inverter needs to turn on when the array starts producing, but the battery can’t charge without the backed up loads being powered, and the backed up loads can’t be powered until there’s enough battery charge to supply the inrush current.
A DC coupled system like the Powerwall 1, RESU, or pretty much any lead-acid system doesn’t have this problem at all.