After no answers for a long-term solution, I have developed a solution called the WP247 Extension Notification System. It is comprised of two plugins that are in the WordPress plugin directory:
- A “Server” plugin called WP247 Extension Notification Server that runs on the extension developer’s website to compose and distribute notices.
- A “Client” plugin called WP247 Extension Notification Client that runs on the extension user’s website to retrieve, display, and dismiss notices.
See this article on the WP247 Extension Notification System for more information on how it works.
That handles the notification side of things. I ran across this article called Beta Testing WordPress Plugins with WP-Rollback and will use this approach for beta and release candidate testing going forward.