Thanks to the flurry of news generated by the recent update I decided to give DF another shot (the computer I had when I first heard of DF was sadly not up to snuff at the time), and it has turned out to be a very addicting game. So one week in I figured I'd toss up the suggestions I've compiled.
Please excuse me if some/all of these have been previously suggested to death, the search function on these boards has given me many false hits on words and seems to ignore the date restriction.
Water:
Water spread- Weight spreading of water to tiles based on their 2d pathing to a z-level drop, weigh drops filled with running water highest.
Grooved tiles- A tile condition (like muddy or smoothed) that has a higher weight for water spreading than other tiles (though less than the weight from z-level drops), and/or is treated as having 1 less depth of water for spreading calculations of adjacent tiles. Created by dwarves and a chance when water spreads from a tile.
Raining- Any tile with a view of the sky has a small chance of creating a 1 deep square of water, and a bigger chance of adding 1 to any contained water (up to 7). Vary the intensity of rainstorms, so light rains create little water while a hurricane will flood the place. Tiles that allow water to flow through still create water on them, it just falls through instantly.
Rain conditions in the embark screen could display like surroundings are, by frequency and intensity of storms. So an area with infrequent/light rain would be shown as Desert Conditions, while a frequent heavy rain would list as Hurricane Alley.
Damming- Allow building of walls and floodgates into place 1 z-level below the builder if through a hole. (yes, I know this one has been suggested before, I just felt the need to voice my support)
Flow control- Variable rate flood gates (yes I know it's been suggested) and variable rate drains (combine floodgates and hatches).
Roofs- Floor tiles that have a designated flow direction (always treat the adjacent tiles in the flow direction as having 1 less water depth than it actually does, while tiles in the other direction are counted as having 1 more level of water than it actually has). Take longer to build, have a lower value, and a higher pathing cost to prevent roofs being used as floors everywhere as the norm.
Waterlocking doors- Allow a locking setting on doors to prevent them from opening if there is a certain amount of water on the other side (set from 0-7).
Plumbing- Saw a couple suggestions already, just tossing in support.
Soil:
Collect soil- Allow collection of other soil types, not just sand. Soil is stored in buckets.
Apply soil- Build option, works like a floor. Uses 5 buckets of soil per square to turn rocky squares into farmable squares. Squares make with silt count as fertilized for their first crop, or just as higher quality soil if farmland depletion gets implemented.
Dirtshop- Workshop built with 1 stone/wood and 1 barrel. Takes 2 buckets of mixed soil, dwarf makes a water run after collecting the soil and soaks to separate the soil into into two buckets. So turns 2 buckets of clay loam into a bucket of loam and 1 of clay. Soil mixes of 3 types separate out one at a time (sandy clay loam into sandy loam and clay). Process loam turns 5 buckets of loam into 2 sand, 2 silt, and 1 clay. Takes a long time to process, especially the loam conversion.
Clayworks- Makes various items out of clay, which must then be baked in a kiln to be usable. Same options as other workshops that use stone.
Glaze shop- Grinds rough glass into glaze, applies glaze to decorate stone and clay items (which must then be baked in a kiln to set the decorations). Higher quality glass yields better results.
Peat- Add option to wood burner to load a bucket of peat along with the wood for either normal operation, adding a helping of ash to the end product (make charcoal makes 1 charcoal and 1 ash, make ash makes 2 ash).
Dwarves
Veinseer noble- Appointed noble position of high respect, uses his superior knowledge of rocks (mining skill) to determine what lies beyond the apparent wall. New designation targets unrevealed squares, which the veinseer to get as close to as possible then try to determine what the square contains (works across Z levels). Range revealing is dependent on the mining skill of the veinseer. Position requires a study.
After a certain population the veinseer position becomes Master Veinseer, requiring a bedroom, dining room, and better study. Having a veinseer master opens multiple veinseer apprentice appointed noble positions (same as the base veinseer position).
Ramtop dwarves- Special civilization not always selectable on embark. Ramtop dwarves have a special flag set that causes them to gain good thoughts from eating rat based foods and bad thoughts from foods containing other meats. They are never disgusted by rats and are highly susceptible to cave adaptation. Ramtop caravans offer lots of rats for sale, and weaponized bread (as powerful as any iron weapon).
Misc-
Exercise wheel- Idle dwarves come here to kill time, generating a couple power points for every dwarf working out.
Skylight- 3 items cut from rough glass, Diffuser, Collector, and Glass cylinders. A diffuser built over a hole, if connected to a collector on the surface via glass cylinders, provides natural light to the room below to help prevent cave adaptation. Not as effective as actual outside time, but better than nothing.