A suggestion with a huge impact, if and when chemicals are introduced into dwarf fortress (Alchemy workshop uses, wink wink nudge nudge, eh?) they should give the player a huge amount of new options.
For example, i've been reading about limestone on Wikipedia, and apparently it reacts violently to acidic compounds. So, it could be possible to destroy limestone objects if acids are ever made and/or sold in fortress and/or adventure mode. The same goes for rubbing /dumping basic compounds on acidic objects /liquids.
Now, it doesn't need to be complex and have Zinc combine with Hydrochloric acid and result in zinc chloride and hydrogen fumes... It could be as strait-forward as a PH system, where 7 is neutral (pure water) and the extremes of the scale (was it 0-14... 15?) are basic /acidic. If the difference is too extreme between objects, they destroy eachother, or just the more neutral one and damage the stronger one.
The outside /underground river could also have PH levels, which could influence farming -- if the mud from the river is too extreme in PH nothing will grow; so using the other water source would be necessary. Maybe if the underground river is acidic, there could be no limestone lining at all, and if it's super-corrosive, dwarves wouldn't swim -- they'd dissolve! ]
[ December 27, 2006: Message edited by: Mechanoid ]