Okay, so I've got three suggestions as the title says:
1. Military Formations - It would be very interesting to see if military formations were implemented. First of all, it would help that my dorfs do not charge in front of one another and get themselves killed. Plus, it would look kill with a line of speardorfs covering a charging wedge of axedorfs. The same could be said of gobbo invasions - if they used formations, maybe it'd be better than lining themselves up for a ballista to the face or simply marksdwarves.
If not formations, at least an order on how spread out they should be. Like "tightly packed," "staggered," "loose," and "no order." This would help even if we didn't have formations.
2. Disease - Right now, disease is limited to Syndromes and a general topic of "Infection." I would really like to see actual diseases implemented into the game, as well as epidemics and pandemics too - this would also affect your fortress if you embark on an area that's been affected by the disease. Diseases could also be transmitted through stagnant water, hunted wildlife, and the diseased blood of enemies. This, of course, could be turned off at worldgen if preferred by the player.
3. Bait - As much as I'd like to micromanage 30 cages to catch some wild animals, I think it would be cool if cage traps could be "baited" with food - be it vegetation like plump helmets, meat, or otherwise. Different types of plants could attract different types of animals, along with the meat. It would be up to Toady how much of each item is required to bait animals in.
Thank you for reading, and have a nice day.