score:4
Finally received an official response from Disney's email support:
A Government-issued photo I.D. (such as a driver's license or state I.D.) or any documentation that has the Guests name and a California address will work as proof of residency.
Also, according to a Reddit comment:
I have heard several people confirm that today they were NOT CHECKING IDs. That could change but they were not today.
So in practice you might not get checked, at least for now.