What would be the impact if assets which were used as collateral in a loan were taxed as cash?

Currently the wealthy can borrow against their stock and other investments.

They do not pay tax on this.

Imagine we put in place a new law: If you’re using your shares as collateral to buy something, you are taxed as though it’s cash. Those are now “committed shares “ And can either be sold or kept—but cannot be used as collateral in a new lending relationship. 

Say I have 400m in MSFT(as one does)

I use that as collateral to get a loan to buy Twitter. The lender now needs to alert the IRS that a taxable event occurred for my shares.

What would this do to our economy? To society?