Route planning but exclusively using established cycle routes

Shameless feature request.

The new Eurovelo route planner enables routes using just the EV routes but nothing else. I'd dearly like to be able to extend that to plan tours just using established cycle routes of any description and nothing else. In the context of cycling.waymarkedtrails.org, just red, blue and possibly yellow and purple routes. Perhaps provide checkbox options for which class of route is included. Of course the user would have to pick start and end points that exist on a recognised route.