Did a quick search, and didn't find that California's exit tax has been passed, only that it's been proposed.
The state already has income tax of over 13% (for reference, Alabama's state income tax is 5% and there are endless deductions), so there might still be a powerful incentive to leave.
Further complicating that calculus is the fact that the income tax is just that...a tax on income. Whereas the exit tax, if it passes, is a tax on wealth, defined as net worth.
Also, the exact definition of "net worth," gets really hairy for the targeted people. As in, it's pretty easy to come up with the value of publicly traded stocks, bonds, CDs, Treasury notes, etc.
But what about privately-held companies? What about special classes of shares in public companies often held by founders and their families? For example, Ford.
What about ownership interest in a venture capital fund?
What about fine art?
What about the present value of future income you'll receive from a trust? What about the trust corpus itself?
Do you tax the present value of Social Security or any pensions? Using what actuarial assumptions? Regardless, would that be in addition to or in place of tax on the income from pensions or SS?
Suppose you own a godamighty ranch in Idaho -- not uncommon among the targets. Does California have jurisdiction to tax you on the value of real estate that isn't even in the state? It didn't when you lived in California, but now that you've moved out of California it does? Really? How does that work?
Net worth is assets minus liabilities. So how do you define liabilities? A bank note is pretty easy. But suppose that among your large portfolio of businesses you own 100% of a given company. You personally guarantee that company's debt, and alone among your portfolio, this particular company is in financial distress. At what level of distress does the guarantee (normally classified as a contingent liability) become counted as a real liability?
This is a clear money grab based on political calculation. The targeted population is really rich people, and there aren't enough of them to truly move the fiscal needle for a state the size of California. Plus, the general public loves sticking it to rich people because....well, it feels good.
So as a politician, you pander to the public, gain the image of sticking it to the rich, and don't lose much in the way of votes -- and if the target no longer lives in California, they can't vote against you anyway.
If this passes (and I didn't find anything that said it has yet), it will be challenged immediately. They might win in California courts, but it would be appealed. And once it gets out of the friendly confines of the California courts, I don't see any way it's allowed to stand.