Sorry I don't know if this topic has already been put forward. Checked the first 10 pages and searched for underground but nothing came up. Just had the idea of an underground area that adds an underground map that is separate from the world map. It just adds another area that can be just as big as the world map and is on the same server. The area would be a new zone for vets mostly because there would have to be a requirement to enter the zone. Either it could be total population or a certain number of cities needed to enter the area. There would also be certain areas on the map that would allow access to the area or maybe some type of research needed to explore as well. The area would be very high level area with many monsters all high level and hopefully new ones that people have never seen before. Also, there would be factions underground. I was thinking maybe a war between dark elves and gnomes or dwarves where you have to choose with who to side and do quests for them.
However, I'm torn between whether there should be cities underground or if there should instead just be outposts you can build where you can rest your army and have to send supplies to from your other cities to keep your army supplied. Since your underground you'd be able to gather much more stone and iron but would not find any wood or food. Make it so npcs also constantly raid your city/outpost so you have to keep it maned at all times or else its possible to lose it. Pretty much give the game a feel where the world is trying to fight back against you and give people a big challenge in trying to hold their own against in the underground. Alliances would play a big part as they may try to hold an entire part of the underground as they slowly worked toward trying to destroy the faction they chose to fight against. But eventually they would have to deal with alliances that had sided with the other side as they clash to protect their allies. This way you can have the huge battles that some people want to have but do not want to start. Finally an outlet for those countless resources and armies that the vets are sitting on.
Sorry even though I'm new I thought that this kind of thing would motivate alliances to be more active with each other and for people to be more active in general. If people have more ideas they would like to add or things that should be changed feel free to comment. This is a work in progress and of course just an idea. Thanks for your time.