That's significantly more complicated for no real benefit. It actually carries a much higher risk for the IRS as the securities are volital.
All you have to do is tax them when they use the assets as collateral, and for good measure tax the loan as income.
You could even throw in a minimum threshold to not apply it to regular people, and force them to pay people more in the process. This can be achieved by setting the threshold to a variable, like 100x the average annual take home pay of the bottom 20% of earners (~$1.6m) and make it a annual total of loans to close the loophole of a bunch of small loans.
If they want cheaper loans people have to be paid more.