The tricky thing about that is the edge cases. Say you're heading due north, approaching the pattern at a busy uncontrolled field. In additon to the swarm of bees in and around the airport pattern, a plane transiting the area south of the field heading due east is at your 10 o'clock position. You're closing on it, so you see it displayed. You cross in front of it, so on your iFly display you see it at your 9 o'clock, and then you start to pull away, and per your request it disappears from tthe screen.
You proceed to immediately forget about it because you're focused on the traffic in the pattern. Deciding that you want to fly a circle to wait for some of the pattern traffic to space out more favoribly for your arrival, you initiate a right 360. As you come around the first 90deg, all of a sudden that plane you forgot about looms large in your windscreen, and iFly suddenly starts barking traffic alerts at you. You have little time to react, and have to take drastic action. Not good.
Maybe if the logic is something like "greater than 5 (7? 10?) miles *and* range increasing, then don't display" or something like that, but the filter criteria needs to be more sophisticated than simply "range not decreasing".