The thing is, farming is only as complex as it is because it makes sense for it to be so, but nutrition is simple because if you had to cover a decent amount of the possible variety, it becomes Dwarf Farm. Soapmaking, smelting steel, manufacturing high-end clothing and working with magma are complex and have decent rewards for people who invest in them, but they're choices. Farming can put all of these to shame if you let it, but making it required would cause the same reaction that I get when a noble tells me to start a metalworking industry because he wants pretty things.
I had a big post written up, but my keyboard wigged out for some reason and saved you from it. The gist of it was that to have steel manufacturing, soapmaking or a high-end clothing industry(weaving dying, clothesmaking) running more or less constantly, you need between five and seven dorfs' worth of work, including hauling for each of them. For farming, per Grower, you're looking at at least ten to fifteen dorfs' worth, depending on how and if you deal with milling, how paranoid you are about roasts rotting in the kitchens, and whether you decide that it's worth having a Wood Burner and Potash Maker. If nutrition was important, everyone would have to do this, and it's not like optional industries like soapmaking where you can just ignore it if you can't be bothered with it, and can let an existing industry lie idle. Farming is always on. Unless you're on a really strict population limit and trade for your food and drink.
As an option in the init file that's off by default, it could be cool, and could be worked in quite well with poisons and disease, probably, but the drain on dorfpower, while realistic given pre-industrial agriculture, would be pretty unpopular.