It would be the opposite of stability though. While I gave the example of US Treasuries as a worst case scenario in reality before we get to them half the finan

It would be the opposite of stability though. While I gave the example of US Treasuries as a worst case scenario in reality before we get to them half the financial system would've been drained to the Fed. People would pull their money out of regular bank accounts and stick it in the Fed even at negative interest rates because a predictable percentage (probably small) loss is better than uncertainty that your bank might fail. That is the complete opposite of stability, it's a worse kind of chaos than what would happen now. There's a myriad of complicated and dangerous side effects from this for a benefit that frankly isn't useful for most people (due to FDIC insurance). So the only people it makes sense for are those relatively rich people who ought to be able to diversify their savings/investments to protect themselves.