Nethack provides an 'Explore Mode' option, which allows you to play without fear of death, at the cost of not getting an entry on the high score list. Thus, if you're a newbie, or just want to fool around, or need to test something, you can enter explore mode and do it safely.
I would love to see something similar for Dwarf Fortress; a mode where your dwarves won't starve, or go berserk, or otherwise send your carefully-laid plans collapsing in ruin. Sometimes you just want to spend a few hours designing intricate networks of waterworks (or lavaworks), or spelling out your name on the map in precious gems, or the like, but it's hard to do that when you have to worry about keeping the dwarves alive.
Since DF doesn't have a high score list, I'm not sure what the tradeoff would be (or if there should even be one). Perhaps you shouldn't be able to enter Explore Mode in worlds already occupied by non-EM fortresses or adventurers, so as not to have an unfair advantage over them? But I don't know how multiple fortresses and adventurers interact in the same world anyways, or even if they can.
(The original impetus for this suggestion was that I had a nifty plan for waterworks interwoven with the halls of my main base, but before I could implement it the hunters started revolting, blood on the walls, dwarves fashioning crude helmets from the bones of their neighbors, and then someone activated the self-destruct system.)