Age of Conan also had areas that were cutoff from the main world, where you could build housing and PvP against other guilds and their forts/housing.
Kinda like Wintergrasp, only if everything was player-made. Every now and then, a staged battle would occur.
WoW could do it like this, I feel. I do agree what with WoW’s zone sizes, housing the SWG way would not work. But it’s been done before.
Either the AoC strategy, or an instance portal you run into that takes you to instanced housing, similar to garrisons to some extent, but entirely indoors.