Off the top of my head some things I'd love to see:
Scaling dwarf hapiness requirements. Your fortress grows, so do the expectation of your dwarves. They'll need more for the same hapiness when the total population increases.. This to give some incentive to develop larger fortresses, get more variety in food and booze etc.
There's immigration. Let's have emmigration. If your dwarves are unhappy with your fortress or they are in an economically bad situation (if dwarven economy is active) they might chose to leave the fortress instead of living unhappy/becoming depressed/enraged and die.
Dwarven religion, let's have shrines and temples to those dwarven gods your dwarves seem to worship. This to give followers of the gods religion a happy thought when they worship in the shrine/temple.
Special dwarven military personel to make the squad more orderly, telling them when they may charge in combat/open fire. If the squad leader dies the dwarves would fight like they do now, unorderly and charging headfirst regardless of strategy at first sight of the enemy. Also siege engineers as military personnel.
Schoolhouses to keep those dwarven children occupied and crush their little spirits.
Non military dwarves to consider the risk when encountering a wild animal and not running away when the creature isn't aggressive or dangerous. No need for dwarves to run away from a lone hoary marmot.
A special designation to build your own roads to connect to another city, like you have in worldgen. This'd cost a large amount of materials depending on the distance to the destination. You'd start constructing one of these at the edge of the map. This would become the new spawnpoint for immigrant and caravans etc.
Multithreading!