Someone saw Mission to Mars recently?
Joke aside i fully agree to this feature, most divers use equipments simmilar to this , they usually average air consumption over a small period of time and evaluate how much time is left at this consumption rate. The math is fairly easy but it is very handy to have it at hand.
Obviously in our case it can add a lot of dramatic feel to mars exploration.
This sort of readout should also be available for the main base air supply.