I selected geology, physics and linguistics.
Given the level of simulation that occurs for rock formations in DF it would interest me to know how it stacks up against real life. Taken to its logical extreme, DF could one day be used as a form of spelunking simulator, with the added bonus of batmen lying in wait. I want to know how far this level of simulation will go, and how it will be modelled.
Physics are useful to any DF player, and the world seems more realistic when various laws of physics can be applied to achieve a specific effect that the game does not reference explicitely - such as drowning traps. I'm interested in how many more physics effects will be placed into the current system. Will steam exist, for example? If it did, would it have temperature and pressure? Could, say, a modified water wheel design be spun by the force of pressurised steam, by dint of it following physical laws? Will towers ever have a chance to collapse if poorly designed? Will items under a drawbridge get partially crushed, holding the bridge halfway up?
Finally, linguistics in DF are nothing short of brilliant. I love the way the game forms words and titles, and translates them on the fly. There are so many questions relating to the future of this field inDF. For example, putting asid ethe matter of implementation, does writing as a concept exist in DF? Could a random language generator exist? Can languages evolve, or slang? Will different species ever borrow words from one another? Are normal languages and kobold gibberish entirely different in implementation, or is there some overlap in how the game makes use of different languages? Can a creature be known by different names?
Oh, should biology be chosen, I'm very curious as to how fantasy creatures are made to coexist in the games engine with normal creatures. Like, for example, the upcoming hydra test. How will a hydra work, apart from just calling it 'magic'? Would, the undead, especially skeletons, have anything in common with living enemies? For example, since they're already dead, how can they be killed? How do their life processes work, and how would they be halted?