Hillary knows that she is hated something vicious. So, there is no penalty for her to go out there and make outrageous promises like that to corner the undecided hedgesitter as well as pander to the crazy left. No matter what she says, there is no way for her to be even more hated by those who already hate her.
This business about taxing the rich is silly in the extreme. Those that are rich enough also have enough money for lawyers and tax evasion schemes. They set up a trust and pay themselves a small annuity out of it, for "living expenses", or they incorporate and do the same in different ways. And these are just the tricks I know about... There are plenty of people that would pay significantly more in taxes if their real income decreased. In reality, the tax increases end up hitting the middle class the worst, relatively speaking, because they are not rich enough to play a lot of the above games.
What we need is a real tax reform, wherein at the least, people or legal entities are NOT taxed for things they already own. Also, many of the services of gov that are currently covered by general taxes should instead be offered as a directly paid individual service.