A yellow crop duster can easily be seen 2 miles out as being yellow, a plane, and if its biplane or single wing. Probably could tell if its a low wing, or high wing cabin type.
Something in camo, that slips along not doing big banked turns, could easily be within 1/4 mile before you could track it due to engine noise. And that's assuming your standing on the ground. It would be a lot tougher in a plane.
Until we have systems that can show us our full peripheral range of movement detection (some 160-170 degrees in most people) Icons will remain a vital necessity.
However, that is not to say that a new icon option would not be worth exploring.
Consider a new arena, where the only thing an icon shows is country. So you have a very small bishop, knight, or rook icon.
No distance, no name, no plane type. Icons show at 3k (same icon setting as current FSO) and if your not looking in the right direction you won't see it. No big neon sign saying "here I come".
The problem is, even if we had this arena, and this setup. What is it going to do to gameplay?
You'd see a lot more cherry picks, a lot more hording (at the least wingman tactics) more HO attacks.
We would probably all be finding WWII silhouette images to study so we would have a better chance of figuring out what we were up against.
Winning would be less about ACM, and flying, and more about approaching unknown bogeys.
Then when that bogey that you stalked for 2 sectors gets killed by some 2 weeker who cares less. Whats going to happen?
Do you see how any of this, however interesting it may be, is good for gameplay as we know it?
Cause frankly I can't see how it will fly.