I will assume this will end up just how banking regulation ends up, the banks makes the same amount of money (or more) and the loss from regulation is made up somewhere else (higher fees, worse interest rates, etc).

Pay-per-download seems to be a very likely future for apps using external payment systems, free or not (which is only fair, you are after all leeching off the App stores in that scenario), charged by Apple/Google to the developer.