1)For me would be wonderful if in Guild u could implement Stash and Vault so we can divide works, will be gatherer that collect resource, workers that craft items and pvp that can use items, it will be like a Bee Hive.
2)Another beautiful feature would be the guild Hall or HeadQuarter where people can socialize training or chatting or work in labs(alchemy weaponsmith etc)or prepare war and this improvements could be buy by Guild King and Queen then owners, different kind of room, labs tavern or War Council for example.
3)Furthermore u could add boats, Guilds could own more boats create a fleet and do sea battles with other Guilds, each boat could be equipped with items.
Regards