I think it will be a few months before factions and private servers are implemented. Addons/mods will be added with private servers and I believe limited to that medium.
Here are links to information about factions and private servers.
If anyone has found current information regarding clan implementation, let us know.
So far I’m enjoying the player population restriction in each world/server, but I haven’t heard how that will affect private servers. I know private servers will be able to adjust the level of PVP.