I myself have no idea how to make an add on or anything so I will just put forth my idea and perhaps somebody will. I want an add-on that puts a circle on the ground surrounding my aircraft of a certain distance unit, like a nautical mile. Almost like a radar, but you see the distance lines on the ground in real time. This would help at estimating the distance of certain locations on the ground by eye, which is useful. The idea is, eventually you wouldn't need it anymore, and would be proficient at doing this. I don't know about you guys, but I think it would be a good idea.
If you don't understand what I'm trying to say, just ask and I'll try to make a picture.