I think it would be nifty if DF were the type of game that, once established, could be left for a time while your dwarves managed themselves. Many of the original Maxis games were of this nature (ie. simcity, simtower, simant).
Heh, I happen to be the type of player that likes to see his creation control itself at some point. I enjoy games with a goal of, "Did I design it well enough to support itself?" An example is designing a pet dungeon in Dungeon Keeper 2, setting constant invasions on and seeing how long you'll hold out.
The hurdles as I see them, are food production and immigration during the early stages. I propose an Agricultural Noble that gives you the ability to select a planted plot as "renewable". This means that every season it is queued up for replanting and regrowing of the originally selected crops.
Immigration can be handled via the init file, or you could just decide to not let your fortress run itself until immigration was finished and your setup was solid. Mandates could become a hassel while you're gone. Perhaps an option to have the dwarfs auto-produce mandated goods or something...
I'm not familiar enough with some of DF's inner workings to know if other factors must be accounted for. Outlasting the sieges, tantrums, moods and other random occurances is the fun - seeing if you designed a fort that can withstand such random events.
Now I'm not proposing this so you can just leave the game on all week as your dwarves level up and make you phat loot. My whole perspective on the topic is one of design. Can I design a fort that if left overnight, will still be there in the morning? If only the food wasn't such an issue, I could see that being a reality.
What are other peoples' thoughts on the matter? I used to leave DK2 running all the time on my spare computer. I'd glance over and see the little fellas dancing disco to "burn baby burn" or my bile demons sprouting gas clouds at some hapless guards that wandered in. I realize DF wasn't designed for what I have in mind. But, perhaps with just a slight tweak here or there, it could become a reality?