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.

_renderNewRootComponent: function(
    nextElement,
    container,
    shouldReuseMarkup,
    context
  ) {
    
    
    
    warning(
      ReactCurrentOwner.current == null,
      '_renderNewRootComponent(): Render methods should be a pure function ' +
      'of props and state; triggering nested component updates from ' +
      'render is not allowed. If necessary, trigger nested updates in ' +
      'componentDidUpdate. Check the render method of %s.',
      ReactCurrentOwner.current && ReactCurrentOwner.current.getName() ||
        'ReactCompositeComponent'
    );
    invariant(
      container && (
        container.nodeType === ELEMENT_NODE_TYPE ||
        container.nodeType === DOC_NODE_TYPE ||
        container.nodeType === DOCUMENT_FRAGMENT_NODE_TYPE
      ),
      '_registerComponent(...): Target container is not a DOM element.'
    );
    ReactBrowserEventEmitter.ensureScrollValueMonitoring();
    var componentInstance = instantiateReactComponent(nextElement, false);