That would be different from bitcoin lending schemes that already exist. The collateral's value in dollars has to stay above a threshold, and if it falls below that, you have to add more collateral or get liquidated and lose some of your btc. An example you can investigate yourself is Ledn's bitcoin loans, where you post btc collateral to borrow dollars to buy more btc. Cool idea... But some people have lost that bet. I would not assume these wall street parasites will be more benevolent. People will ape in at the top of the market, then the bank will legally steal their btc.