[atmavatar]

A much better tax change would be to automatically realize gains on stock used as collateral in loans.

That would cover loans the ultra-wealthy use for their day-to-day living as well as loans used for leveraged buyouts of other blocks of stock (usually to buy or become significant voting shareholders of a particular company).

The other side of things would be to start actually enforcing anti-trust laws. A big part of the reason we have people running around with 10^11 dollar wealth is due to extreme market consolidation.