Not to disagree with the notion of change to cost (I have no idea what it'd change), but just to satisfy some geeky urge.... I wonder how expensive it is to revise an engine management system these days?
In the early electronic systems, air con just upped the idle and ran a little rich (or in the case of my tractor engine, just pulls on the throttle cable a bit
). By the mid 90s, the ECU would make more direct changes to compensate for the compressor, such as including cutting the clutch at WOT.
The developed engine maps go through months of testing in all sorts of climates and are extraordinarily complicated. With the level of integration of ancillaries like aircon into modern management, it might be quite a task to develop a system for the rare non-aircon order.