Coming from the official FAQ...

Q: Why is there a new Clan system for Call of Duty®: Ghosts?

A: Clans in Call of Duty®: Ghosts will include deeper in-game integration and more features, from in-game Clan Management and Clan–specific playlists to the all-new Call of Duty® Clan Wars game mode available in the new Call of Duty® app. This year also introduces cross-platform Clans, allowing players to create and/or join a single Call of Duty®: Ghosts Clan across the following platforms: including Xbox 360, Xbox One, PlayStation®3, PlayStation®4 and Windows PC.

@BagirovEmmanuel I am basing it on this document, which does not list Wii U as supported by the Clans system: http://t.co/81ZKyYCOuF

— Dan Amrich [1oS] (@OneOfSwords) October 29, 2013

Thanks to Autosaver for the heads up!