Actually, on that topic...
Is it currently slated for animals of different sizes to require eating different amounts of food? If elephants and hoary marmots eat the same amount of food, but give off radically different amounts of meat when butchered, then it produces a rather silly comparison of which animals are the most effective to raise...
Well, in the case of Elephants, they take a while to grow up...
Even newborn elephant babies are worth insane amounts of food, though. You can just do the mermaid thing and keep some breeding stock, and then slaughter the infants. It is, in fact, something I do on some of my "experiment forts", since it's much easier to just mod elephants to be purchased at embark, and feed my dwarves elephant meat all day every day than it is to work on setting up a proper fort, and it lets me get right down to what I was experimenting on in that fort.
What are the complications with this? We already have metal stored as units (150 iron instead of 1 bar). So I'm curious what the blocking factor is. Lingering old code?
Well, this is something I went over pretty extensively in the
Volume and Mass thread...
Basically, almost every object type already has a volume, and every material type already has a density. The displayed mass of every object is derived from these two things.
The primary problem with implimenting Volume and Mass fully is that it requires Stacking to work. (That is, the thing on the top of the ESV, which I'm assuming Toady has been putting off because he's had trouble coding it before.) If we start using .1 kg of brass to make a brass earring instead of an entire 17.5 kg bar (2 liters), then we are using fractions of a unit, and that means that dwarves will need to start learning to put fractions of bars back into piles with other fractions of bars, again. Otherwise we wind up with the same problem we have with coins - a whole bunch of .03 kg of brass lying around the fort with no reaction that uses that small a quantity, but it takes up a whole tile in a stockpile, anyway.
The concept that you give quantifiable dimesions to tiles is also potentially involved in that, which means that it can lead to things like a rewrite of the liquids code so that water, for example, is measured in volume, as well. Quantifiable dimensions to tiles also means multi-tile trees and monsters, which is always one of those big game-crashers.
Of course, all of these things are pretty much necessary for the game going forward. Stacking is on the devpage (Toady just wants to do Caravan and Military arcs first), and liquids code needs some optimization and the ability to allow in other liquids like oil, as was mentioned in the last Q&A round. It's just that Toady is prioritizing other topics that he probably thinks are more fun.
(Which sounds cooler, invading other fortresses or getting mead, or making fluids take up less framerate?)