I would love something akin to Strava segments, but not as random or arbitrary. For example, I live in Wales which has a continuous open path all the way around the coast line and i’d love to be able to see what percentage of it I’ve run. This ‘segments’ feature could be for well known and established named trails, paths and routes rather than just anywhere.
I’m sure a major issue is that these may not be included in the map data that is pulled for CityStrides so the nodes may not exist, but this is a fantasy feature after all!
That’s funny … a while back I made this ‘Routes’ feature, but I did a really bad job and nobody used it. 
You could take an Activity and turn it into a Route, and then people could compete on those Routes.
So that’s how I got around the problem you noted - this data wasn’t in the City/Street/Node, it was Strider/Activity generated. I think that’s part of why it didn’t really take off, though … it was super specific to each Strider.
For your use case, specifically - you’ve got a continuous open path all the way around the coast line … I’m assuming that this is not present as a single ‘street’ in CityStrides. Is it present at all?
Maybe another way to accomplish this is to allow people to ‘group’ Streets…
The tricky thing with that path in particular is that it wan’t built as a single path, it’s been plotted along streets with nodes when it goes through towns, and then most often just trails and footpaths which don’t have nodes at all. We have a lot of great paths close to me that have been made in a similar way, mostly following rivers and valleys, but they would all be hard to plot too.
I also wondered about other famous routes like the Appalachian Trail but of course they would span multiple ‘cities’ which may complicate things further.
I agree turning a single activity into a ‘Route’ is problematic, and a bit too specific and very much depends on consistent GPS.