Check me on this. Wing A/I does not affect the aircraft approach performance singificantly. It WILL affect the MISSED approach CLIMB gradient. At most places the required minimum missed approach gradient is so shallow that with wing A/I on or off the resulting actual gradient is way above the minimum.
Variable approach minima is in use where any kind of thermal A/I derrived from engine bleed source is considered. Chambery LFLB is one example.
Mr L