Let's start at $1B. I cannot think of any earthly reason a single individual needs more than $1B worth of wealth. After all, the US presidency apparently only costs $250M to buy.

I would fully support a 100% wealth tax for everything over $1B.

Now, of course, the implementation of such a thing would be enormously complicated. There are a million places to hide your wealth, squirreling it away behind shell companies and dark LLCs which you or a designated agent are a controlling member of.

But in concept, I cannot fathom why a human being could possibly say, "You know, $1B really isn't enough for <this>."