We're switching Atom to React, but we want to support backward-compatible shims to our previous view framework.

In the old framework, views were represented as jQuery-wrapped DOM elements. Ideally, we'd like to provide backward-compatible shims by simply rendering the React component and wrapping its root element in a jQuery wrapper with an API that's compatible to our old editor views. That would essentially look like this:

``` javascript
var editorRoot = document.createElement('div')
React.renderComponentWithRootElement(Editor(props), editorRoot)

// the element would actually be wrapped in a custom subclass of jQuery,
// but this is clearer for this example
var editorShim = $(editorRoot) 
```

Currently, this isn't possible because React components need to be rendered into a container. So instead we need to create a wrapper element and render the component inside it. This is sad because it adds an extra layer of markup which confuses styling, and also means that the editor has a wrapper when used via the shim layer but no wrapper when embedded as a child via React itself.

Is there something fundamental preventing React from adopting DOM nodes directly without the parent? Is this something we could even hack in in a way that would be somewhat maintainable?

:heart:

render() {
        return <div />;
      }
    }
    const container = document.createElement('div');
    const instance = ReactDOM.render(<Component />, container);
    
    
    expect(instance.updater.isMounted(instance)).toBe(true);
    ReactDOM.unmountComponentAtNode(container);
    expect(instance.updater.isMounted(instance)).toBe(false);
  });
  it('warns if findDOMNode is used inside render', () => {
    class Component extends React.Component {
      state = {isMounted: false};
      componentDidMount() {
        this.setState({isMounted: true});
      }
      render() {