Would love to see this for the SF Bay Area - lots of great cycling around here and I'm unsatisfied with using Strava to create routes!
One of the most frustrating things for me with snapping to official paths is not being able to modify it for common workarounds (for instance, going across the Golden Gate bridge, everyone takes a shortcut through a parking lot, but every map routing platform I have used forces me to go the official route and messes up my nav)