The end game should have a lot going for guilds, they are a great way to extend the lifetime of the game and can create a dynamic world.
Sieges for important territory of valuable resources could be implemented for the largest guilds, allowing them priority over said resources and tax on market transactions occurring in the area. The actual mechanics of sieges could be lifted or innovated from similar concepts like BDO.
For the world, individual PvP between guild members could grant the player fame in the guild, allowing them to be noticed by guild leaders (Being given ranks/rewards from leaders). If guilds could declare war against other factions, kills could grant guild tokens to be used alongside in-game currency to purchase siege weapons or camps building up to a final battle.
Guilds could control what areas are used for what, creating residential areas, infrastructural areas, trading districts, etc. This wouldn’t be hard to code, beacon like barriers that display certain areas named as certain districts wouldn’t actually do anything but display what areas are for what. The way to enforce this would be up to the guild, allowing no inherent way to force areas to be used for specific situations could create a police job, furthering the economy. One thing must be present, when a player places a beacon in a guild area, a notification for the player that would say that there is a certain purpose for the area because the guild could remove the beacon if they don’t believe it suits the purpose. To balance this out the guild would have to have influence/guild tokens to be able to ‘restrict’ the area.
Kills could count towards or against influence in an area, like a pie chart the influence of factions would be split by percentage. It could be determined by player count, kills, $$$ investment, blocks placed by players, and other factors. Influence could give a general idea of the leading factions. On launch most areas would be mainly influenced by the central guild, other guild would quickly be able to establish influence and eventually surpass the central guild’s influence.
An arena could be designated in major cities of guilds that could be used for entertainment for spectators and competitors, earning the guild money and more influence. Other matches could be held as another way to settle disputes, individual matches with stakes, two guilds could use a champion each, representative of the guild and fight for disputed land.
Guild rewards (for beating other guilds/having a large influence) could include additional infrastructure for guild use and a general array of random useful tools that could be community suggested. Control of other guilds (partly/completely,permanently/temporarily).