Clans are undergoing yet more revisions for their spot in Call of Duty: Ghosts. Activision has outlined some of the major changes to clans, which include PC support and cross-platform clans.
A lengthy FAQ summarized by the One of Swords blog details the changes. Among the bigger changes, your clans aren't separated by platform, so you and your friends can earn XP together no matter what your console or PC preference. That also means clans are coming to PC, naturally, and each platform will support it on their respective launch days.
Clans are limited to 100 players, and you can only be in one clan at a time. But, you can leave anytime you want to start your own or join another. You can reserve your existing clan name now if you're already an Elite leader, as long as it doesn't conflict with someone else who has already registered that name from having it on another platform. That's just what happens when you merge them all. Clan names will be given out on a first-come, first-served basis.
The FAQ also promises that clan support is more integrated, and you can start a clan or tweak settings from inside the game menu itself. Any two clan members working together can earn clan XP, so you don't need to grab a large group. Clans will also level up faster. The bad news for Wii U players is that the console isn't mentioned in the supported platforms for clans, and the FAQ explicitly says it's not planned to work with the app.