It's not. Since home prices are linked to interest rates (prices go up/down depending on interest rate movements), all that's going to happen is that home prices will go even higher. In the end your monthly payments is going to be the same.
The bank takes it's share in the form of fees. The negative rate is simply because the money market sees negative rates on the 5-10 year horizon. The bank simply passes the rate of the money market on to the consumer:
> Høegh said Jyske Bank is able to go into money markets and borrow from institutional investors at a negative rate, and is simply passing this on to its customers.
Negative bond rates happen when there is a surplus of capital looking for "safe havens". Some investors are willing to pay to have money placed safely for a number of years. The Danish real-estate bonds are regarded as a very safe haven.
It is actually a sign that something is very wrong with the general economy.
Negative rates only happens when investors shy away from stocks and just want their money to be safe for the next 5-10 years. Investors are actually willing to pay just to have their money kept safely out of the stock market. What does that tell you?
There is so much volatility (read: Trump). Stocks can both go up and down with a tweet. Until the next day or 4 hours later. So investors flees stocks and look for safe bonds.