Any computer running CUPS 1.5 or later supports IPP Everywhere. For now that basically means all major Linux distributions, Open Solaris, *BSD, and OS X.
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.
Printers supporting the final IPP Everywhere specification should start appearing in 2016.
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.