A2 has an incredible number of systems to test. However one of the long term gameplay systems in the game remains the nodes and their development/fall. The game will likely have significant upheaval during node progression during server start however determining the psychology of players and predicting how they interact with nodes months after finishing nodes development is nearly impossible to predict but extremely important. The way players siege is likely to change from month 3 of the server when every ZOI can become a metro to month 9 when every ZOI is already vassalized and likely to change again months later when the novelty of sieging is less prevalent and primarily driven through in game rewards and politics. It is entirely possible for sieges to be completely gamed once a server has finished its node vassalization, additionally even if its not gamed it may not happen nearly as often as would be healthy for the player economy. So below is my idea to change it and prevent that from ever being an issue in the first place.
I bring this up because with relic shards being earnable in a node war, node superpowers being realized with a single metro and the value of a metro to its players being so high, its very possible that sieges become a rarity after the server has a finished vassal structure and has been finished for months.
Edit:
This idea is based around node wars and only occurs after a successful siege of a METRO, no other successful siege would use this.
My idea to change the ZOI vassalization structure as it stands. Remove every single nodes lockout ZOI after a successful siege of a metro. Then allow each previously vassalized node to gain ZOI territory through node wars, expanding territory would then create a series of mat and exp sinks for the players of the node that successfully won that territory. I would suggest creating some sort of npc caravan line that would run between the acquired territory and the node that took it with the predicate for players to defend those caravans or risk losing that territory. As that territory expands nodes inside that territory are vassalized and any territories they had taken in their attempt to become the next metro added to the winners territory pool further adding npc caravan supply lines.
IMPORTANT -> A node can forfeit its right to territory expansions through a common vote by its citizens. Doing so would automatically place it in a vassalized state again to a nearby node that was intending to fight to expand its territory to become a metro.
this structure gives any node level 3 and higher that was previously vassalized by the metro a fighting chance to become the next metro. In the case by some miracle a level 3 node won the territories and took over the ZOI of the metro it would follow the standard vassal structure. Basically instead of there being a level 6 node at the top of that vassalization structure for awhile it would be a level 3 node. Of course it would be allowed to progress unlike the vassalized nodes around it and so overtime it would go from 3->6

Feedback, thoughts, ideas?
This idea uses already implemented systems - the NPC caravans already run for castles and their taxes, and the node territory wars are already being implemented as well.