"It has always resulted in a string value": only MACOSX_DEPLOYMENT_TARGET always took the form of a non-integer. The code for sysconfig.get_config_var() has a pretty clear intent: it will try to cast its return value to an int.

I don't have a strong opinion whether this is fixed this way or another. I would think, however, that there are surely places in existing code that expect and rely on sysconfig.get_config_var() returning an int for integer-type values.