Denmark has introduced a negative interest rate mortgage. That's an interesting one because if you borrow $200k today and only owe $195k in 10 years, what happens?

First, since you don't have to make payments, you can't default.

If you can't default, why bother with qualification?

If you don't have to qualify, is there an upper limit to how much you can/should borrow?

If there's no upper limit and you never have to pay, it doesn't matter whether the seller charges $100k or $1M or $10M.. it demonstrates that the entire system is entirely made up.