Dev Log #1
Here's a rough draft map I am playing around with:

So, when Archcrystal ends the dwarves are at war with ALL goblin civilizations in the world, as well as all the civilizations near to them. Even though none of these civs are destroyed they are all very depleted as far as population goes. Even with Archcrystal disappearing they still have a military of hundreds of steel armored dwarves, who are now completely leaderless. So, what I foresee in this time skip is that basically the whole map has been remade by the destruction that ensued.
In this setting the dwarves, goblins and the original civilizations around Archcrystal have all been destroyed over the passing of centuries, and the ruins of which are settled by new peoples.
Why Archcrystal isn't simply reinhabited later?Well, consider that Archcrystal sits in the middle of a cursed jungle. Clouds come in regularly that turn the living into super powered and berserk undead. It would be fair to argue that even getting to Archcrystal is an ordeal itself.
Conveniently, the only thing next to the fortress is a dark pit on the map, and in my head canon the goblins developed those trench works so they could try and clear a path to Archcrystal to siege it.
Still, with the collapse of everything these paths would be lost and getting to Archcrystal would be near suicide, and the jungles are probably filled with these berserk super undead.
What kind of campaign will it be:This should be a heist. Heists are fun because they tend to rely on planning and improvisation.
With AC (shorthand for Archcrystal) being lost and in such a dangerous place, AND being near impregnable itself half the fun will be getting there!
So, the campaign starts with the assembling of the team (the players) and the beginning is about players traveling to gather information to access AC, because they need a route and a way into the fort itself. Any other info they learn could also be useful and the campaign should reward players who put a lot of effort into extra research.
For example: Learning about AC's front gate defenses could save the party from having to learn about those traps firsthand.
Sub-Class TalkNow, the previous post discusses adding sub-classes, but I think rather than that it should have specializations and that these should all be from dwarf fortress
Each player picks a specialization their character has and it will in some way contribute to the heist.
For example:
Miner - Opportunities to dig around obstacles
Siege Engineer - Able to access and use siege weaponry and defenses
Mechanic - Repair, disable and set up machinery and defenses
Ranger - Bonus to sense of direction checks such as traversing AC or the route to it
Animal trainer - Ability to interact with, pacify or even tame certain encountered creatures
We'd make a more full list and the players pick one each, giving a lot of replayability options