Here is the google maps example that I am trying to copy in Esri: https://developers.google.com/maps/documentation/javascript/examples/directions-draggable .
Here is the closest example I have seen with Esri: http://esri.github.io/quickstart-map-js/html/directions/routes_and_barriers.html
If Esri has a better or different way of changing the route then I would be up to hearing about that but to me dragging the route and putting in new "Way Points" makes senses.
If this functionality does not exist and you know when this functionality will be available, I would also like to find out about that.
Thanks! Alfie