Any computer running CUPS 1.5 or later supports IPP Everywhere. For now that basically means all major Linux distributions, Open Solaris, *BSD, and macOS.
Mobile devices running Android 4.4 and later come with native support for IPP Everywhere. Prior versions of Android are supported using an installable application.
The IPP Everywhere Self-Certified Printers page lists printers that have been registered on the PWG web site.
The Wi-Fi Alliance has developed a Wi-Fi Direct Printing specification, based in large part upon IPP Everywhere.
The PWG IPP workgroup has developed specifications for scanning and facsimile, and is currently developing a specification for managing the whole printer. These will be combined with IPP Everywhere to create an updated IPP Everywhere specification to support accessing all of the services of a multifunction printer without special software.
The current specifications, mailing list, and archives for IPP Everywhere are available on the PWG IPP workgroup page.