Add breadcrumbs of some sort to the map while riding or running to show where you’ve been. Some bike computers with GPS have this feature. Maybe just turn the road from black to blue or yellow, whatever? I can see dots for other zwifters moving over the black road. Just highlight it for where I’ve already ridden.
Does not have to be persistent from ride to ride upon initial release. Have as option to show previous breadcrumbs so you can later complete your adventure.
Future revisions could offer a badge as route or map explorer for having ridden every road in a route / map / world, etc.
Example: I like to explore on a map while riding. By highlighting where I’ve been will allow me to turn and choose another road to explore. After ending a ride I was shown a map that I missed a small section of road. Remembering every road while riding is extremely difficult. Makes it more challenging and another way to keep people interested in zwifting