Wouldn’t this ‘negative cash’ be a regular financial instrument like a stock short, reverse mortgage, credit default swap, etc., which they actually can use, pr

Wouldn’t this ‘negative cash’ be a regular financial instrument like a stock short, reverse mortgage, credit default swap, etc., which they actually can use, precisely because nothing is created by this process? It is just less liquid than hard cash, which can affect the perceived trade-able value (but that too is already factored in as expected interest).