We should be able to look at see if the child has a data-react-id attribute but isn't rendered by this copy of React and consequently warn.

See https://groups.google.com/forum/#!topic/reactjs/mdwfKKJ0L2Q.

},
  /**
   * Take a component that's already mounted into the DOM and replace its props
   * @param {ReactComponent} prevComponent component instance already in the DOM
   * @param {ReactElement} nextElement component instance to render
   * @param {DOMElement} container container to render into
   * @param {?function} callback function triggered on completion
   */
  _updateRootComponent: function(
      prevComponent,
      nextElement,
      nextContext,
      container,
      callback) {
    ReactMount.scrollMonitor(container, function() {
      ReactUpdateQueue.enqueueElementInternal(prevComponent, nextElement, nextContext);
      if (callback) {
        ReactUpdateQueue.enqueueCallbackInternal(prevComponent, callback);
      }
    });
    return prevComponent;
  },
  /**
   * Render a new component into the DOM. Hooked by hooks!
   *
   * @param {ReactElement} nextElement element to render
   * @param {DOMElement} container container to render into
   * @param {boolean} shouldReuseMarkup if we should skip the markup insertion
   * @return {ReactComponent} nextComponent
   */