First watch these videos to have a better understanding

https://www.youtube.com/watch?v=mMvubbX-SHg&t=2s - Ashes of Creation "Nodes" part 1

https://www.youtube.com/watch?v=44HChA1Kkfk "Nodes" Part 2

Where would this take place? (Maps)
Guilds can establish their cities either on the surface of cradle or on the different depths or near sub towns.

Guild halls vs Guild cities? (open discussion suggestion)
Should Guild halls act as their own cities? or should Guilds have to 'combine' (Each guild hall will still be independent and have their own halls) Concept of each guild acting as their own cities or multiple guild halls being in 1 city?

Trade routes: The ability to build trade routes to other guild halls or guild "Cities" (Note: It would make sense to at least be able to develop cities at this point since the Knights have been at cradle for so long) Those guild halls are able to trade resources (Materials or weapons for crowns or energy?) These trade routes could also be plundered by other guilds and trading guilds can protect their trade routes/caravans by sending guild members or paying NPC Knights to defend them!

Siege/Declaration of War: Guild cities can initiate sieges of other guild cities. Cities can have alliances with other cities. Independent guilds that help other cities with sieges, a city that has multiple guilds in it and has 1 guild participating in an active war WILL not draw in the rest of the guilds in that city into war. But each guild that is in that city should have a feeling of having a duty of having to defend that city. If there are no online players in a city/guild while a siege is happening. The loot received by the attacking guild will either be halved or only receive a small percentage of loot.

Destruction of cities
Should guild cities be able to be completely destroyed? Or just de-leveled and looted?

Dormant halls There is a strong possibility that a guild would just fall off and never return to life. For this reason, at least 1 guild master position should be democratically elected. This would allow that guild master to be able to attract new members to that guild or just completely disband it so that it doesn't take up space in the city. Or if a guild only has 1 member (the guild master) and that member has not been active for at least a year. That guild will lose its physical structure in the city and be moved back to Haven.

Guild City expansion: In the video, there is a city and the city center has a "Castle" looking apparatus. The 'guild city' can have it's center be its guild hall. While also being able to make additions such as a Bazaars, arcades, Auction houses and squares similar to Haven. Guild cities could have a plot of land be designated for housing where members could design their own houses. OR plots of land where they can designate another guild to have their guild hall (alliances? Sister guilds?) The size of a guild city should be proportional to the size of how many members it has not how deep their pockets are. For this reason, it would be ideal for guilds to share cities. More members = more expansion/land

ALSO, I'm not asking to copy the entire concept of Ashes of Creations. But I think actual city building and competing with other players instead of just PVE is going to make this game more interesting. In conclusion, can we have a competitive city building/trading concept that allows players to compete for resources added to the game?

Lots of Unanswered questions!
How do guilds in the same city interact with each other? Who makes decisions in that city?
How are members of a guild going to participate? What is their role in a city?
How do cities act with each other? How do monsters act with cities?
How will the voting system work in a city or guild with no members?

While I don't have the immediate answers to these questions. I'm hoping someone would help contribute to this idea to help it become more developed.