Just some things I've thought of, I'd like to hear other people's things that I'm sure I've missed, but these are just some things I've noticed that I think would fit, and am somewhat surprised aren't in the game. For these things I'll attach information about why I think they're applicable to be in the game. I know additions to the RAWs are low priority, but I figured I'd give some input.
Cupronickel: Atlantis / 3rd century BC Greece through Roman Empire / 1st Century BC China through European Renaissance (European rediscovery around 1600 AD, and individual recognition not until the 1800's alongside the distinction of Nickel as an independent metal) - 60/40 through 90+/10- mixes of copper/nickel (modern 70/30 is generally the strongest mix ratio, used in shipbuilding and highly corrosive environments, while Chinese weapon alloys were generally 75/25, the same mix used in many modern coins including the American five cent Nickel. Other mixes see extensive use in parts expected to see a lot of weathering, as an example 80/20 is seen commonly in the automotive industry.) And was used for weapons/armor for the wealthy. Equal in value to gold by the Greeks and Romans and one of the two copper alloys known to them as Orichalcum, and was known as "white copper" to the Chinese. In China it was used occasionally in swords for the wealthy until high quality steels became common and more commonly used as dinnerwear for the wealthy, whereas in Greek/Roman society it was on rare occasions again used in weaponry, otherwise used as a white decorative metal and used in currency. It is roughly 30-40% stronger than a traditional bronze alloy. The main issues with cupronickel comes from the scarcity of readily-available nickel ores, aside from rare deposits. China got most all of it's ore from a single mine - in which the white nickel ore was called Yunnan, named after the region/mine it was found in, while the end result alloy was known as paktong. This mine was heavily guarded as a result of the unique properties of the ore (and was bright white on it's own within the stone layers, likely being what led to the mine's existence in the first place). The greatest flaw was from ancient cultures not recognizing nickel as it's own, independent metal. But Dwarves dig deep and can access larger quantities of the ore, and know what nickel is, even going sofar as to make a decorative variety of this metal in the form of "German Silver" / "Nickel Silver". So why don't Dwarves also get the ability to make the weapon quality alloy variant? True, it was not a common choice, with leaded and arsenic bronzes nearly matching it in strength while being far cheaper in human history, and iron being more readily available, but it was historically used for such activities, and I see no reason why dwarves, with their knowledge of the metal, and dwarves being dwarves, would not attempt to find an alloy mix which could be weaponized. And there isn't really any reason it can't be. (EDIT: Comparisons at bottom of post)
Arsenic and leaded bronze: Innovations in the mid-bronze age, Arsenical and leaded bronzes were alloy mixes which added further strength to a more traditional bronze mix, generally by 20-30% improvement. While arsenical bronzes were a simpler process, they lost popularity in modern times due to well... the poisonous arsenic. Leaded bronzes are less of an issue, and most notible of leaded bronze alloys is likely gunmetal. I honestly don't see why dwarves don't have this an option as both a way to 'cut' bronze with other metals, but also to give, alongsie cupronickel, an extra option for a no-iron or low-iron embarks as a higher quality metal. Alternatively as a middle-ground between iron-quality metals and steel.
Cobalt: Nearly identical to iron in structural strength (somewhat stronger), cobalt is.. an interesting part on this list. Cobalt was not isolated as a metal from any of it's ores till well past our technology cut-off date. However this is less due to technological reasons other than Humanity just not finding out how to refine it. While the easiest and most common modern methods do involve electricity, sulfurous cobalt ores, such as cobaltite, can be refined purely through smelting methods, albeit ones which require higher temperatures than iron. That said, our dwarves smelt Adamantine, steel, I could go on... so this isn't of issue. The other issue is the requirement to smelt multiple times in this process and clearing the slag each time - the sulfur and arsenic are procedurally removed in this fashion, leaving just the cobalt. Generally speaking though it takes, as previously stated, multiple cooling and remelting phases to purify the cobalt to a useable state, since after the arsenic and sulfur are removed, it is necessary to remove the iron from the mix via oxidation in slag form of the iron. While not mechanically doing much... we have all that cobaltite everywhere. I want to weaponize it to be honest, and well... I'm fairly certain Dwarves, who don't mind working in sulfurous environments like magma forges, would mind working with sulfurous cobalt alloys, unlike humans.
Smalt glaze: We have tin glazes in-game, and now comes another Chinese invention which made it's way west. While the Chinese did keep the production process largely a secret from the west until after our cut-off, there is no technological barrier that would have kept a European glazer from using cobaltite in a pottery glaze as the Chinese did. Very popular in it's time and even today, cobalt blue colored glazes are among the most valuable glazes for pottery there is, and offers another use for all that unused cobaltite in-game.
Celadon glaze: Another Chinese-sourced pottery glaze, this time utilizing iron oxide - i.e. hematite. This is an even older and more wide-spread pottery glaze, resulting in a jade green coloration. While invention of the glaze can be sourced to China in the 1st century AD, it was produced in the middle east at least by the 12th century and in Europe by the 16th century. I'm a bit more surprised this is not an option in comparison to Smalt given that this was more common throughout history.
Iron sand: Red sands are in almost every occasion, red due to the inclusion of iron oxide. Through smelting in the presence of flux, iron may be isolated readily. This process was an important source of Japanese iron production for much of it's history. While not highly developed in many regions worldwide given the greater difficulty of production in comparison to otherwise readily available ores. Having this as an option added into the game would allow for aquifer and low ore embarks more viable, assuming of course the chance for red sand. Though this is a bit more questionable in my mind than the above examples I suppose, yet at the same time I feel it should be an option as the process wasn't exactly unknown to europe within the technology limit. It's just that red sand wasn't exactly common in europe, and generally speaking it just would be cheaper to obtain a traditional iron ore which would take significantly less effort to utilize.
Ceramics from Peat: while a rather less common source of pottery, peat is nonetheless able to be fired into a useable ceramic known as Torbite in modern times, which while not as durable as stoneware, shares the property of being non-absorptive and therefore water-safe, although the difficulty of firing peat without setting the peat on fire may be a barrier to it's inclusion.
Borax as flux: It has been for much of history, an important flux in iron production... I just kinda wonder why it's not in DF.
Beds from other materials- Aside from the premise of making trees be necessary to dwarven society, I don't quite get why we don't have other options if we look at things realistically, such as.
A: Stone; Romans had stone beds for peasants in many cities, including a carved in stone pillow. (usually covered with whatever they could to make them softer) I can't think of something more dwarf worthy.
B: Metal springs; Dwarves can make complex mechanisms and gear assemblies, as well as pressure plates. Which means Dwarves know how to make springs. I'm fairly sure dwarves could figure out they could make a bed by connecting springs along two sides of a metal frame.
C: Hammocks: About as simple as can be here, isn't it? Tie off two ends of a large cloth?
And for the bit more out there things:
Scale armor: being a mid-point in strength of plate armor and the flexibility of chain armor, scale was used for... quite a good bit of history. The scales could be made of anything from rawhide and horn, leather and metal, or even ceramics and paper! Notably cheap to produce in comparison to chain or plate, scale was less popular due largely in part to it's durability in question, along with the fact it was largely ineffective in comparison to the popular combination of plated mail. Lacking the rigidity of plate or the ability of chain to divert edged blows, certain Chinese (all the chinese stuff, I know, but you can't blame them for being more dorfy than dark-age Europe) varients, namely paper and ceramic, traded the ability to stop blades or multiple blows in favor of being better than most any source of projectile - Mythbusters having shown the ability of the paper armor, and more modern versions of the ceramic armor being known as Dragonskin - one of the strongest bulletproof vests there are, able to stop high-power rifle rounds. Though I am aware that scale would probably need to be an addition and the more exotic flavors are unlikely to see inclusion, it still strikes me as odd we don't see the more primitive civilizations, and even the dwarves, utilizing this cheaper technology for infantry bodyarmor.
Nethercap pykrete: With a fixed temperature below the freezing point of water, this just somewhat suprises me, that in all dofiness, this is not a thing. Aside from it's temperature and rarity, nethercap logs act the same as any other wood in dwarf fortress. I would think at some point in time a dwarf carpenter would try washing away the sawdust with some water and would find froze after working on nethercap. He/she would then find that they couldn't break the ice resulting from it. he/she would then do the dorfy thing of trying it in a bucket and find that unlike ice, pykrete (hereby called nethercrete) does not shatter readily, and instead acts like stone. This carpenter regains is honor among his people for finding away to turn water and trees into a dwarf-suitable material. I would consider this as something to be included as:
A- More building materials. One unit of nethercap wood would equal about eight times as much end material of netherkrete. (the standard pykrete mix is 1/7.25th wood pulp)
B- It could easily be cast. Given Nethercap is just beneath the freezing point of water, it would harden slowly - enough so it would be simple to pour it into whatever mold you wanted, and then the mold could be reused after creating whatever. This means you could make anything from simple furniture to something as complex as armor with it, as well as tools and most objects you could want. Granted, it isn't as strong as metal, but like the nethercap wood in it, I would think it would hold a fixed temperature, and therefore useful for dragonslaying and hunting down fire imps and the like. Or it could be used for magma-proof mechanisms and floodgates.
C- It's strong. Pykrete, while having about half as much compressive and impact strength in comparison to concrete and marble, it is more resistant to tensile forces, though not to the extent of wood. Yet in terms of strength / weight it is quite attractive, being quite close to regular ice in density - making it 1/3rd as dense as most stone.
D- Dragonproofing. Not many other options for suitable materials that I can think of. Sure, you could do the same with regular nethercap but obviously there is the issue of getting enough nethercap in the first place. Plus if/when walls and bridges become destructible, it would probably survive longer than wood.
And for other things which I am going to simply list for one reason or another, or are more minor and have shorter explanations.
Anthracite - metamorphic layer coal.
Most any metal into a bolt - I don't see a practical reason why I can't make bolts from sterling silver or aluminum, while we can make them from Adamantium.
Brass- Used in weapons nearly as long as bronze in areas where tin was scarce. Why can't we use it for weapons/armor if we can use copper?
Antimony & Arsenic - we have their ores, the former being as useful as lead is currently, and the latter being useful if we include arsenical bronze.
Morningstars - why don't dwarves get these? I think they're a rather dorfy weapon personally.
Medical training - So why can we only train doctors on living, injured dwarves? And not animals, corpses, goblin prisoners, or "volunteers"?
Leaded glass - Kinda a thing for middle ages Europe. So... yeah been wondering for quite some time why it's not in there.
Clubs - maybe an actually kinda-sorta useful-until-you-get-something-better wooden weapon option?
Kite and tower shields - So we have a buckler (which are mostly from even later than our timeline cutoff, mind you.) and a standard shield (probably a round shield.) So why not a larger kite shield / heater shield and/or an even bigger tower shield?
Chain coifs and gauntlets - we have chain for our torsos and legs... why not for hands and head? They're timeline - friendly. And I'm fairly certain Urist McRandomdwarf would prefer a broken finger to having it fly off in an arc.
But those are just my ideas/questions I figured I'd bring up for the sake of officially asking about them and suggesting them. I know I probably should have gone through past threads and the like, but eh, I figured I'd ask outright about everything I've been thinking about at once.
Edit: Below I'm adding a table comparing strength of modern alloys to use as a comparison, with the highest strength choices I can find being available given in-game mixes. (ex. Bronze is a high-tin bronze, no other additives)
Metal | Modern Alloy Name | Tensile yield | Tensile Strength | Elasticity Modulus | Brinell Hardness | Density | Shear | Chemical
Copper | (N/A, Annealed) | 33.3 MPA | 210 MPA | 110 GPA | 35 | 8.96 | 48GPA | 100% Cu
Bronze | C90700 | 172 MPA | 290 MPA | 103 GPA | 80/105* | 8.77 | 50 GPA | 88% Cu + 12% Sn
*cast/hammered
Gunmetal | C90500 | 172 MPA | 303 MPA | 103.5 GPA | 75 | 8.72 | 52 GPA | 86% CU + 10% SN + 3% Zn + 1% Pb
Iron | Wrought | 159 MPA | 236 MPA | 210 GPA | 105 | 7.95 | 70 GPA | less than 3% Carbon, remainder Fe.
Cobalt | (pure) | 225 MPA | 760 MPA | 211 GPA | 125 | 8.80 | 75 GPA | 100% Co
Cupronickel | C71300 (cast) | 103 MPA | 538 MPA | 152 GPA | 121 | 8.94 | 57 GPA | 75% Cu, 25% Ni
Cupronickel | C71500(annealed)| 166 MPA | 392 MPA | - | 95 | 8.95 | 57 GPA | 70% Cu, 30% Ni
Cupronickel | C71500(cold worked)| 411 MPA | 490 MPA | - | 130 | 8.95 | 57 GPA | 70% Cu, 30% Ni
Cupronickel | C71500(tempered*)| 483 MPA | 517 MPA | 107 GPA | 150 | 8.95 | 57 GPA | 70% Cu, 30% Ni
*ATSM B151 H04 temper (Same as MIL C15726F for military specification)
Steel | AISI 1060 (RH*) | 485 MPA | 814 MPA | 205 GPA | 241 | 7.85 | 80 GPA | 99%+ Fe, 0.6% Carbon, less than 0.4% Mn
*Rolled homogeneous. Strength is close to the average for 13th century European sword steel.
http://www.myarmoury.com/feature_bladehardness.html