There are a few statements from people I read again and again, as well as a few facts of DF, and they seem to fit together well into a comparatively easy to implement feature, with far reaching implications: Adding a roguelike mode, or in DF terms an "arcade adventurer mode" or "adventurer challenge mode" somewhere in between adventurer mode and Arena Mode.
I obviously am not too knowledgable about the code base of DF, and I have no experience with programming roguelikes, but to a causal observer, it seems like it's a doable project considering the existing features of DF.
Anyway:
People love DF for a lot of unique features, but looking at it from a roguelike perspective, DF has a few things that make it different from most roguelikes:
the depth of the movement/combat/wound/personality system, solid procedural generation systems for a lot of different environments, and ease of adding new creatures, armor materials and so on.
On the other hand, it's not very convenient to play DF like a roguelike: You need to generate a world, make an adventurer, and then spend the rest of your weekend finding a dungeon to begin with. Endlessly travelling the world map, stopping every five minutes to eat and drink. Finally you find it just to get lost in it and most likely never encounter interesting creatures to battle.
Personally, I love those simulation-y aspects of DF, and they're the reason I keep coming back and am invested deeper than with any other game. But sometimes you just want to do some dungeon crawling. And why use some other roguelike when DF already has all the elements you need, just not assembled in the right combination?
So my suggestion is as follows:
Add new roguelike mode:
- generates a small, simple (compared to DF worlds) dungeon
- uses existing procedural generation algorithms to create several levels in a fixed order (for example: village with small keep >> sewers >> catacombs >> labyrinth >> caverns >> hell)
- fills it with stronger and stronger random monsters and increasingly better loot
- Uses the same character creation as adventurer mode
- permadeath
The question, of course is, how and when this could be implemented and whether adding a new mode (which doesn't need to be hooked up with other modes) is really as trivial as it seems. Even then I assume "trivial" would still be something like a year of development time, which is hard to justify for an entirely new mode at this point in development.
Still, maybe adventure mode moved away quite a bit from the vision it was at one point; having your adventurer check out your own fortress and relive it's history. With adventurer mode and fortress mode growing together more and more (which IMO is the best thing that can happen to DF), there's more and more of a gap left that a "roguelike mode" could fill. Especially serving as both introduction (learning the mechanics without having to worry about navigating the world of DF), as well as challenge for experienced players, it could improve two weaknesses of DF: tutorial and endgame.