Just an Idea
Maybe Aircraft manufacturers should design and incorporate an "unreliable airspeed switch" into their aircraft. And add it as one of the memory items in case of suspected unreliable airspeed.
the way it could work is simply to write an algorithm which takes some known accurate values such as current pitch, power, weight, configuration and altitude (gps or otherwise), etc, and calculate a 'predicted' speed value based on the above values remaining constant. The switch would cause the speed bug to be replaced by a predicted speed bug (different colour)
This would require training pilots in the interpretation of the predicted speed info and the limitations/inaccuracies associated with the system.