I would hope that there isn't any 'extra income' for banks arising from all this. Surely the change in receipt of income is only a timing difference?
Here is an example...(taken from kiwiblog) and it's just one scenario.
Let’s say you live in Auckland and have just brought a house at the median price of $875,000. You have the 20% deposit so take out a mortgage for 80% or $700,000. Assume a 25 year term and you get monthly repayments of $3,891 and total interest paid of $467.248.
Now let’s say you take the six month holiday. Your $700,000 owing grows at 0.375% a month so at the end of that six month holiday you owe $715,898.
You continue paying $3,891 a month but it now takes 27 years to pay off your mortgage, not 25 and the total interest paid is 501,450.
So you end up paying $34,202 more in interest.