node.php

<?php

/**
 * links = {
 *     "canonical" = "/node/{node}",
 *     "delete-form" = "/node/{node}/delete",
 *     "edit-form" = "/node/{node}/edit",
 *     "version-history" = "/node/{node}/revision/{revision}",
 *     "admin-form" = "/admin/structure/whatever..."
 *   }
 */

Subscriber.php

<?php

class MySubscriber  implements EventSubscriberInterface {
  public function __construct(EntityManager $entity_manager, LinkRelationshipManagerInterface $manager) {
    $this->entity_manager = $entity_manager;
    $this->manager = $manager;
  }
  
  public static function getSubscribedEvents() {
    return array(
      Routing::DYNAMIC => array(array('onDynamicRoute')),
    );
  }
  
  public function onDynamicRoute() {
    $collection = new RouteCollection();
    foreach($this->entity_manager->getDefinitions() as $entity_info) {
      foreach ($entity_info['links'] as $relationship => $pattern) {
        $relationship_plugin = $this->manager->createInstance($relationship);
        $route = $relationships_plugin->getRoute($pattern, $entity_info);
      }
      $collection->addRoute($route);
    }
    return $collection;
  }
  
}

  public function onDynamicRoute($collection) {
    foreach($this->entity_manager->getDefinitions() as $entity_info) {
      foreach ($entity_info['links'] as $relationship => $pattern) {
        $relationship_plugin = $this->manager->createInstance($relationship);
        $route = $relationships_plugin->getRoute($pattern, $entity_info);
      }
      $route_name = $entity_info['name'] . '.' . $relationship;
      if (! $collection->has($route_name)) {
        $collection->addRoute($route_name, $route);
      }

    }
    return $collection;
  }

That seems like a sane addition to the overall code and gives us the ability to overwrite route defaults by simply writing them at the *.routing.yml level.