If and when TouchID makes its *cough* triumphant *cough* return. I honestly doubt it will add much, if anything to the cost of the iPhone.
Apple have been trimming as much fat as possible recently with their pack-ins. Removing chargers, EarPods and reducing packaging.
Sure, they say it’s for environmental purposes and I’m sure to a degree that is true. But I’ve always thought that the removal of those items is for two other purposes as well. 1. Increase profit margins (naturally). 2. Allow for the incorporation of new hardware and technologies, without the need to increase the (already high) cost of the premium products.
But time will tell I suppose.