While I appreciate the integrated route builder, I still mostly use other route builders for their better capabilities (e.g. Garmin Connect or Strava, for easy dragging of parts of the route, popularity heatmap, elevation profile…).
I know that some sites similar to citystrides have chrome plugins, that overlay missing streets/areas on top of those route builders. That makes it incredibly easy to plan routes. Right now for citystrides, I usually have CS opened in one tab and the route builder in another, switching between the two, which is tedious.
Now I have absolutely no idea how hard such a plug-in is to code, but I’d absolutely love it.