This would not be a bad option to have. Yes, some dint need it (as most keep friendly and enemy icons on all the time) but it would be a feasible option if not forced onto others in the MA.
At simplicity sake it could be as basic as adding another line of "if/then" code into the keypress section. However, I have a feeling the icons and ruff distance display are built into the same function and may require separating the two into different references, which isn't quite as simple but not beyond reason.
I'd be willing to support the option but there are still a few bigger fish to fry with AHIII before I see them paying much consideration to another option adjustment. That being said, if it isn't too difficult to add an option in flight preferences or what have you the coder may surprise you with the request sometime.
I hope hitech and the gang come back with a response for you at somepoint.