The banks?

Who wants a 30 year one

Someone who can’t afford the payments on a 30-year mortgage

I’d take one, depending on the interest rate. A fixed rate mortgage is a great thing, because it is a rare opportunity for inflation to work FOR you. The monthly payments are fixed for 30 (or 50) years, while the currency and the home’s values inflate over time. Eventually, the monthly payments become a negligible expense.

The State

I'd like a 300 year mortgage

The bank.

Who wouldn't at the right price?

Borrow all you can and pay back one penny on the dollar.

I should add if it's priced in fiat. If it's priced in BTC, HELL NO