The biggest issue with this idea is that EK Fealty is completely separate from guilds. While it's likely that guild mates will swear fealty to each other, it's not enforced. Even worse - you can swear fealty to unlimited numbers of kings.
To be honest, at this point my care for Eternal Kingdoms is pretty damn low, and I think they missed the boat by making them solely social hubs with no meaning. They could have been used to really bind the campaigns and create continuity. Hell, even as a social hub, they could have been used to reinforce your social choices, but instead they're just going to be a place to circlejerk your epeens between campaigns.