As always, why is the magic number a billion dollars? And how do you draw the line in regards to stock ownership, prevent a founder from owning a certain amount of stock once its value exceeds a billion dollars?
There are several ways to accomplish taxing the mega-rich that don't require rewriting the laws of the universe. It's just that nobody in charge, because they're either the mega-rich themselves or puppets of the mega-rich, wants to address it.
Are you seriously okay with the ultra rich living by completely different rules than everyone else? I think it's probably underestimated how much they get away with not paying.