Would be awesome if guilds could conquer land in "low security areas" then build settlements, extract precious minerals etc. Other guilds could attempt to conquer them or forge alliances. Thus this generates vibrant player driven Guild PVP and PVE gameplay.
I would also add the ability to collect taxes and set laws on the given territory. Taxes from NPC's workers and players doing business in this area.
How should this work in the game? There is a strong focus on story and quests. How I can do a quest if the area I have to go to is owned by a PK-guild? So I cannot continue in the story as areas are controlled by guilds and i cannot enter without getting beaten up? This wouldn't work.
This could work in a sandbox PvP only game (like Eve online for example). But I don't see, how this could work in a story driven game, where players of different gamestyles have to be combined without penalizing a group (PvP vs Pk vs Non PvP vs Permadeath vs Full Loot vs RP vs Group Coop Players vs Soloers).