You don't even need to be that rich. Schwab, for example, has a SBLOC (their "Pledged Asset Line") that requires enough assets to pledge for a loan value of $1

You don't even need to be that rich. Schwab, for example, has a SBLOC (their "Pledged Asset Line") that requires enough assets to pledge for a loan value of $100k. Certainly out of reach for a lot of people, but way lower than Musk-level borrowing. And I expect there are other brokerages with lower minimums. Of course, the interest rates are pegged to SOFR plus a spread, so they're not great right now, though a little better since the Fed lowered rates. IIRC Interactive Brokers offers lower rates.