User blog comment:G0LD3NF1RE/The Elder Scrolls Online QuakeCon Gameplay/@comment-3124449-20130806032812/@comment-3124449-20130806121456

They said that once you finish your character's normal faction, you can do a second faction's questline, and a third after that. They added this because people did not want to be limited to their home territories when exploring. They haven't released many details on this, and I hope that they decide to scrap the idea.