To whom?

I share your concern, although I think a stiff estate tax is enough to break up dynasties, because the brain that arguably earned the billions isn't earning them any more. But a lifetime cap just isn't workable. Would you allow the shares to be put in a foundation? Could the donor have a say in what the foundation does? Who would decide what is allowed or who gets what?

Who should own the discounted present value of the profits realized by an Amazon in the future? The Social The Security Trust Fund? The national Treasury? How would that affect public policy toward corporations?

I'm all for "breaking up" integrated monopolies. Google doesn't need to own Chrome or self-driving, and Amazon doesn't need to own AWS (or maybe it needs to own the highly profitable AWS but not the retail biz). But "breaking up" AT&T didn't make anyone less rich. Only taxes can do that. And taxes need to be levied and the proceeds spent. How would that work?

I had a cousin who died at the age of 100 five or ten years ago. His mother was in fact a communist. When she was in high school - around 1900, in the time of the robber barons - she was assigned an essay: What would you do if you were given $1,000,000? She wrote that if she were given $1,000,000, she would spend it to make sure that no one ever had $1,000,000 again. Plus ça change...