Those not invited to join the beta testing can still do so by finding a device profile leaked online via third-party websites. Speaking of beta testing, what has happened to HomePod users here is exactly the reason why most people should not install beta software on their smartphones or tablets. Since betas are considered to be unstable with plenty of bugs possibly lurking in the background ready to cause havoc.
To make matters worse, under Apple’s terms and conditions, the company is not responsible for any damages caused by a beta version of the operating system. If the logic board on your HomePod ends up looking like the volcano on the hibachi cooking table at Benihana, you literally have no recourse.