The complete insanity of Warren's Wealth Tax plan:
1) As a tax upon wealth rather than income under the 16th Amendment the plan would face immediate constitutional challenge as not be apportioned among the states as required by the Constitution.
2) If, by some miracle, it survived that constitutional challenge, the tax being a tax upon wealth and not income would fall under the "takings clause" of the Constitution requiring them to be compensated for the property taken by the government.
2a) The market value of that money taken would naturally be exactly the amount of tax collected: e.g. if they taxed Bill Gates $100 billion, then they would be required by the Constitution to pay him $100 billion for the property taken, netting the government $0.