In practice, I wonder if there'd be a grace period, e.g. your insurance doesn't kick in until you've lived in California a year. However, since so many jobs start your insurance benefits on day 1, I'd expect this would have to as well.

On the other hand it could still work if the benefit is only available to Californians who have lived there for X years. Not sure about the legality of this though -- states can discriminate this way for in-state University tuition, but in Zobel v. Williams the Supreme Court ruled that Alaska couldn't pay out Permanent Fund dividends based on how long you had lived in Alaska (https://en.wikipedia.org/wiki/Alaska_Permanent_Fund).