Contributors on the upcoming WordPress 4.3 release are moving full speed ahead with plans to improve the experience of using the customizer. They’re also exploring ways to re-architect it to make way for feature plugins that would bring in additional functionality.
WordPress core contributors have continually demonstrated a commitment to improving the customizer to make it better for everyone, and the Theme Developer Handbook was recently updated with a comprehensive guide to using the Customizer API. Plugin developers are also finding new ways to extend the customizer to support the increasing number of users who depend on it for live previews.
Customizer Theme Resizer is a new plugin that is immensely useful for previewing your site on various mobile devices while adjusting options in the customizer. The plugin was created by Japanese web developer Tatsuki Ohta, who has 10 other extensions listed in the official directory. It allows you to review your design for responsiveness without having to leave the customizer panel.