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:

state = {};
      static getDerivedStateFromProps() {
        return null;
      }
      componentWillMount() {}
      UNSAFE_componentWillReceiveProps() {}
      componentWillUpdate() {}
      render() {
        return null;
      }
    }
    expect(() => ReactDOM.render(<AllLegacyLifecycles />, container)).toWarnDev(
      'Unsafe legacy lifecycles will not be called for components using new component APIs.\n\n' +
        'AllLegacyLifecycles uses getDerivedStateFromProps() but also contains the following legacy lifecycles:\n' +
        '  componentWillMount\n' +
        '  UNSAFE_componentWillReceiveProps\n' +
        '  componentWillUpdate\n\n' +
        'The above lifecycles should be removed. Learn more about this warning here:\n' +
        'https:fb.me/react-async-component-lifecycle-hooks',
      {withoutStack: true},
    );
    class WillMount extends React.Component {