There are some lenders that allow you to use your stock portfolio as collateral to purchase a home.
Say for example you have a million dollars in a diversified portfolio and with to buy a $700,000 house. A lender may allow you to borrow against the portfolio and use both the stock portfolio and the house as collateral for the loan. The catch is that if the value of the stocks were to fall enough the lender can sell the stocks to pay for the loan. The same is true if you were to fall behind on payments.
In theory the same kind of arrangement would be possible for bitcoin.