Last time I looked, the interest is negative if you get a mortgage that floats. However, they’ll add some fees that are also a percentage of the remaining loan,

Last time I looked, the interest is negative if you get a mortgage that floats. However, they’ll add some fees that are also a percentage of the remaining loan, so that you are in effect are still paying interest. So no, it is not capped, but the interest has to become even lower before the interest on your Mortgage helps pay itself off.