I see there is no shortage of suggestions!
I've always thought it would be nice if a track could alternate between red and white (or any two colors, doesn't matter) to indicate distance. Some printed maps use this technique, and it's when a TF map is printed for the field where it comes in handy. All a user has to do is count the number of segments to get a quick ESTIMATE of the distance to the next map feature. (I know track distances, particularly user drawn ones, are not precise).
Although there are potentially a lot of options that could be included (colors, distance interval, thickness, etc) I'd aim for the simplest implementation to see if the feature is useful to users. For example, a special track option that draws a red and white line with 1/2 mile (or kilometer) alternating color segments. If useful, more work could be done to integrate it into the regular track drawing routine.
Steve