"Fun" aside, they should take a page from GRRM, and look at what makes popular fantasy fiction so popular, and borrow some elements from there (such as allowing nations to commit atrocities during worldgen). The occasional godly intervention makes things more interesting as well.
From a developer's perspective, though, there is a lot of "fun" left in their codebase. They handle massive pathfinding, temperature and fluid mechanics, and other resource intensive algorithms. From what I remember (I last played DF2010), there is a lot of room for improvement, and the community has discovered several "workarounds" that reduce the workload for common structure types (such as a lava pump)
I just genned a world where the southern elves were crushed for 70 years by a goblin Civ. 3 queen regents and princesses were put to the sword.
The 4 iteration, resulted in Ivis Voidwinds (or something), the new elf princess who promptly went to explore the wilds and tamed giant dingos, lions, polar bears, bears and a host of other animals.
In 162 she led an army and attacked the goblin civ, pillaging 3 cities in an unstoppable attack till they signed a peace treaty in 163.
In 163 the goblins broke the treaty, at which point she waged war till 250, when world gen stopped. She was victorious in battle and converted 5 conquered sites to Elfdom.
She did this all with only 1 kill to her name, she was a high master strategist.
From a developer's perspective, though, there is a lot of "fun" left in their codebase. They handle massive pathfinding, temperature and fluid mechanics, and other resource intensive algorithms. From what I remember (I last played DF2010), there is a lot of room for improvement, and the community has discovered several "workarounds" that reduce the workload for common structure types (such as a lava pump)