Except that net worth is not reported to the IRS et al.
Short of a radical new privacy invasion, they won’t know who owns how much.
Worse, net worth is an ill-defined concept in law. Should net worth reporting be required (I don’t see how), an awful lot of “rich” would soon not be, as they downgrade homes to $900,000 and relocate savings to non-cash forms. (Recall some movie where the rich bad guy is asked where he stashed all that wealth: “See this cane? it was Charlie Chaplin’s. You get the idea.”)
And remember that once you reach “rich”, money can be redirected as needed. Favorite example: Steve Jobs’ salary was $1.
I guess, then, they'll just have to go with the "employed Caucasian" tax. It's really what they want to do anyway.